What’s New In Python 3.4

What’s New In Python 3.4¶
- Author:
R. David Murray <rdmurray@bitdance.com> (Editor)
This article explains the new features in Python 3.4, compared to 3.3. Python 3.4 was released on March 16, 2014. For full details, see the changelog.
See also
PEP 429 – Python 3.4 Release Schedule
Summary – Release Highlights¶
New syntax features:
No new syntax features were added in Python 3.4.
Other new features:
Newly created file descriptors are non-inheritable (PEP 446).
command line option for isolated mode (bpo-16499).
improvements in the handling of codecs that are not text encodings (multiple issues).
A ModuleSpec Type for the Import System (PEP 451). (Affects importer authors.)
The
marshal
format has been made more compact and efficient (bpo-16475).
New library modules:
asyncio
: New provisional API for asynchronous IO (PEP 3156).selectors
: High-level and efficient I/O multiplexing, built upon theselect
module primitives (part of PEP 3156).statistics
: A basic numerically stable statistics library (PEP 450).
Significantly improved library modules:
New
pickle
protocol 4 (PEP 3154).multiprocessing
now has an option to avoid using os.fork on Unix (bpo-8713).email
has a new submodule,contentmanager
, and a newMessage
subclass (EmailMessage
) that simplify MIME handling (bpo-18891).The
inspect
andpydoc
modules are now capable of correct introspection of a much wider variety of callable objects, which improves the output of the Pythonhelp()
system.The
ipaddress
module API has been declared stable
Security improvements:
Make newly created file descriptors non-inheritable (PEP 446) to avoid leaking file descriptors to child processes.
New command line option for isolated mode, (bpo-16499).
multiprocessing
now has an option to avoid using os.fork on Unix. spawn and forkserver are more secure because they avoid sharing data with child processes.multiprocessing
child processes on Windows no longer inherit all of the parent’s inheritable handles, only the necessary ones.A new
hashlib.pbkdf2_hmac()
function provides the PKCS#5 password-based key derivation function 2.Retrieving certificates from the Windows system cert store support for
ssl
.The
ssl.SSLContext
class has a lot of improvements.All modules in the standard library that support SSL now support server certificate verification, including hostname matching (
ssl.match_hostname()
) and CRLs (Certificate Revocation lists, seessl.SSLContext.load_verify_locations()
).
CPython implementation improvements:
Leveraging PEP 442, in most cases module globals are no longer set to None during finalization (bpo-18214).
Please read on for a comprehensive list of user-facing changes, including many other smaller improvements, CPython optimizations, deprecations, and potential porting issues.
New Features¶
PEP 453: Explicit Bootstrapping of PIP in Python Installations¶
Bootstrapping pip By Default¶
The new ensurepip
module (defined in PEP 453) provides a standard
cross-platform mechanism to bootstrap the pip installer into Python
installations and virtual environments. The version of pip
included
with Python 3.4.0 is pip
1.5.4, and future 3.4.x maintenance releases
will update the bundled version to the latest version of pip
that is
available at the time of creating the release candidate.
By default, the commands pipX
and pipX.Y
will be installed on all
platforms (where X.Y stands for the version of the Python installation),
along with the pip
Python package and its dependencies. On Windows and
in virtual environments on all platforms, the unversioned pip
command
will also be installed. On other platforms, the system wide unversioned
pip
command typically refers to the separately installed Python 2
version.
The pyvenv
command line utility and the venv
module make use of the ensurepip
module to make pip
readily
available in virtual environments. When using the command line utility,
pip
is installed by default, while when using the venv
module
API installation of pip
must be requested explicitly.
For CPython source builds on POSIX systems,
the make install
and make altinstall
commands bootstrap pip
by
default. This behaviour can be controlled through configure options, and
overridden through Makefile options.
On Windows and Mac OS X, the CPython installers now default to installing
pip
along with CPython itself (users may opt out of installing it
during the installation process). Window users will need to opt in to the
automatic PATH
modifications to have pip
available from the command
line by default, otherwise it can still be accessed through the Python
launcher for Windows as py -m pip
.
As discussed in the PEP platform packagers may choose not to install these commands by default, as long as, when invoked, they provide clear and simple directions on how to install them on that platform (usually using the system package manager).
Note
To avoid conflicts between parallel Python 2 and Python 3 installations,
only the versioned pip3
and pip3.4
commands are bootstrapped by
default when ensurepip
is invoked directly - the --default-pip
option is needed to also request the unversioned pip
command.
pyvenv
and the Windows installer ensure that the unqualified pip
command is made available in those environments, and pip
can always be
invoked via the -m
switch rather than directly to avoid ambiguity on
systems with multiple Python installations.
Documentation Changes¶
As part of this change, the Installing Python Modules and Distributing Python Modules sections of the documentation have been completely redesigned as short getting started and FAQ documents. Most packaging documentation has now been moved out to the Python Packaging Authority maintained Python Packaging User Guide and the documentation of the individual projects.
However, as this migration is currently still incomplete, the legacy versions of those guides remaining available as Building C and C++ Extensions with setuptools and Building C and C++ Extensions with setuptools.
See also
- PEP 453 – Explicit bootstrapping of pip in Python installations
PEP written by Donald Stufft and Nick Coghlan, implemented by Donald Stufft, Nick Coghlan, Martin von Löwis and Ned Deily.
PEP 446: Newly Created File Descriptors Are Non-Inheritable¶
PEP 446 makes newly created file descriptors non-inheritable. In general, this is the behavior an application will want: when launching a new process, having currently open files also open in the new process can lead to all sorts of hard to find bugs, and potentially to security issues.
However, there are occasions when inheritance is desired. To support these cases, the following new functions and methods are available:
See also
- PEP 446 – Make newly created file descriptors non-inheritable
PEP written and implemented by Victor Stinner.
Improvements to Codec Handling¶
Since it was first introduced, the codecs
module has always been
intended to operate as a type-neutral dynamic encoding and decoding
system. However, its close coupling with the Python text model, especially
the type restricted convenience methods on the builtin str
,
bytes
and bytearray
types, has historically obscured that
fact.
As a key step in clarifying the situation, the codecs.encode()
and
codecs.decode()
convenience functions are now properly documented in
Python 2.7, 3.3 and 3.4. These functions have existed in the codecs
module (and have been covered by the regression test suite) since Python 2.4,
but were previously only discoverable through runtime introspection.
Unlike the convenience methods on str
, bytes
and
bytearray
, the codecs
convenience functions support arbitrary
codecs in both Python 2 and Python 3, rather than being limited to Unicode text
encodings (in Python 3) or basestring
<-> basestring
conversions (in
Python 2).
In Python 3.4, the interpreter is able to identify the known non-text encodings provided in the standard library and direct users towards these general purpose convenience functions when appropriate:
>>> b"abcdef".decode("hex")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: 'hex' is not a text encoding; use codecs.decode() to handle arbitrary codecs
>>> "hello".encode("rot13")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: 'rot13' is not a text encoding; use codecs.encode() to handle arbitrary codecs
>>> open("foo.txt", encoding="hex")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: 'hex' is not a text encoding; use codecs.open() to handle arbitrary codecs
In a related change, whenever it is feasible without breaking backwards compatibility, exceptions raised during encoding and decoding operations are wrapped in a chained exception of the same type that mentions the name of the codec responsible for producing the error:
>>> import codecs
>>> codecs.decode(b"abcdefgh", "hex")
Traceback (most recent call last):
File "/usr/lib/python3.4/encodings/hex_codec.py", line 20, in hex_decode
return (binascii.a2b_hex(input), len(input))
binascii.Error: Non-hexadecimal digit found
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
binascii.Error: decoding with 'hex' codec failed (Error: Non-hexadecimal digit found)
>>> codecs.encode("hello", "bz2")
Traceback (most recent call last):
File "/usr/lib/python3.4/encodings/bz2_codec.py", line 17, in bz2_encode
return (bz2.compress(input), len(input))
File "/usr/lib/python3.4/bz2.py", line 498, in compress
return comp.compress(data) + comp.flush()
TypeError: 'str' does not support the buffer interface
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: encoding with 'bz2' codec failed (TypeError: 'str' does not support the buffer interface)
Finally, as the examples above show, these improvements have permitted the restoration of the convenience aliases for the non-Unicode codecs that were themselves restored in Python 3.2. This means that encoding binary data to and from its hexadecimal representation (for example) can now be written as:
>>> from codecs import encode, decode
>>> encode(b"hello", "hex")
b'68656c6c6f'
>>> decode(b"68656c6c6f", "hex")
b'hello'
The binary and text transforms provided in the standard library are detailed in Binary Transforms and Text Transforms.
(Contributed by Nick Coghlan in bpo-7475, bpo-17827, bpo-17828 and bpo-19619.)
PEP 451: A ModuleSpec Type for the Import System¶
PEP 451 provides an encapsulation of the information about a module that the import machinery will use to load it (that is, a module specification). This helps simplify both the import implementation and several import-related APIs. The change is also a stepping stone for several future import-related improvements.
The public-facing changes from the PEP are entirely backward-compatible. Furthermore, they should be transparent to everyone but importer authors. Key finder and loader methods have been deprecated, but they will continue working. New importers should use the new methods described in the PEP. Existing importers should be updated to implement the new methods. See the Deprecated section for a list of methods that should be replaced and their replacements.
Other Language Changes¶
Some smaller changes made to the core Python language are:
Unicode database updated to UCD version 6.3.
min()
andmax()
now accept a default keyword-only argument that can be used to specify the value they return if the iterable they are evaluating has no elements. (Contributed by Julian Berman in bpo-18111.)Module objects are now weakly referenceable.
Module
__file__
attributes (and related values) should now always contain absolute paths by default, with the sole exception of__main__.__file__
when a script has been executed directly using a relative path. (Contributed by Brett Cannon in bpo-18416.)All the UTF-* codecs (except UTF-7) now reject surrogates during both encoding and decoding unless the
surrogatepass
error handler is used, with the exception of the UTF-16 decoder (which accepts valid surrogate pairs) and the UTF-16 encoder (which produces them while encoding non-BMP characters). (Contributed by Victor Stinner, Kang-Hao (Kenny) Lu and Serhiy Storchaka in bpo-12892.)New German EBCDIC codec
cp273
. (Contributed by Michael Bierenfeld and Andrew Kuchling in bpo-1097797.)New Ukrainian codec
cp1125
. (Contributed by Serhiy Storchaka in bpo-19668.)bytes
.join() andbytearray
.join() now accept arbitrary buffer objects as arguments. (Contributed by Antoine Pitrou in bpo-15958.)The
int
constructor now accepts any object that has an__index__
method for its base argument. (Contributed by Mark Dickinson in bpo-16772.)Frame objects now have a
clear()
method that clears all references to local variables from the frame. (Contributed by Antoine Pitrou in bpo-17934.)memoryview
is now registered as aSequence
, and supports thereversed()
builtin. (Contributed by Nick Coghlan and Claudiu Popa in bpo-18690 and bpo-19078.)Signatures reported by
help()
have been modified and improved in several cases as a result of the introduction of Argument Clinic and other changes to theinspect
andpydoc
modules.__length_hint__()
is now part of the formal language specification (see PEP 424). (Contributed by Armin Ronacher in bpo-16148.)
New Modules¶
asyncio¶
The new asyncio
module (defined in PEP 3156) provides a standard
pluggable event loop model for Python, providing solid asynchronous IO
support in the standard library, and making it easier for other event loop
implementations to interoperate with the standard library and each other.
For Python 3.4, this module is considered a provisional API.
See also
- PEP 3156 – Asynchronous IO Support Rebooted: the “asyncio” Module
PEP written and implementation led by Guido van Rossum.
ensurepip¶
The new ensurepip
module is the primary infrastructure for the
PEP 453 implementation. In the normal course of events end users will not
need to interact with this module, but it can be used to manually bootstrap
pip
if the automated bootstrapping into an installation or virtual
environment was declined.
ensurepip
includes a bundled copy of pip
, up-to-date as of the first
release candidate of the release of CPython with which it ships (this applies
to both maintenance releases and feature releases). ensurepip
does not
access the internet. If the installation has internet access, after
ensurepip
is run the bundled pip
can be used to upgrade pip
to a
more recent release than the bundled one. (Note that such an upgraded version
of pip
is considered to be a separately installed package and will not be
removed if Python is uninstalled.)
The module is named ensurepip because if called when pip
is already
installed, it does nothing. It also has an --upgrade
option that will
cause it to install the bundled copy of pip
if the existing installed
version of pip
is older than the bundled copy.
enum¶
The new enum
module (defined in PEP 435) provides a standard
implementation of enumeration types, allowing other modules (such as
socket
) to provide more informative error messages and better
debugging support by replacing opaque integer constants with backwards
compatible enumeration values.
See also
- PEP 435 – Adding an Enum type to the Python standard library
PEP written by Barry Warsaw, Eli Bendersky and Ethan Furman, implemented by Ethan Furman.
pathlib¶
The new pathlib
module offers classes representing filesystem paths
with semantics appropriate for different operating systems. Path classes are
divided between pure paths, which provide purely computational operations
without I/O, and concrete paths, which inherit from pure paths but also
provide I/O operations.
For Python 3.4, this module is considered a provisional API.
See also
- PEP 428 – The pathlib module – object-oriented filesystem paths
PEP written and implemented by Antoine Pitrou.
selectors¶
The new selectors
module (created as part of implementing PEP 3156)
allows high-level and efficient I/O multiplexing, built upon the
select
module primitives.
statistics¶
The new statistics
module (defined in PEP 450) offers some core
statistics functionality directly in the standard library. This module
supports calculation of the mean, median, mode, variance and standard
deviation of a data series.
See also
- PEP 450 – Adding A Statistics Module To The Standard Library
PEP written and implemented by Steven D’Aprano
tracemalloc¶
The new tracemalloc
module (defined in PEP 454) is a debug tool to
trace memory blocks allocated by Python. It provides the following information:
Trace where an object was allocated
Statistics on allocated memory blocks per filename and per line number: total size, number and average size of allocated memory blocks
Compute the differences between two snapshots to detect memory leaks
See also
- PEP 454 – Add a new tracemalloc module to trace Python memory allocations
PEP written and implemented by Victor Stinner
Improved Modules¶
abc¶
New function abc.get_cache_token()
can be used to know when to invalidate
caches that are affected by changes in the object graph. (Contributed
by Łukasz Langa in bpo-16832.)
New class ABC
has ABCMeta
as its meta class.
Using ABC
as a base class has essentially the same effect as specifying
metaclass=abc.ABCMeta
, but is simpler to type and easier to read.
(Contributed by Bruno Dupuis in bpo-16049.)
aifc¶
The getparams()
method now returns a namedtuple rather than a
plain tuple. (Contributed by Claudiu Popa in bpo-17818.)
aifc.open()
now supports the context management protocol: when used in a
with
block, the close()
method of the returned
object will be called automatically at the end of the block. (Contributed by
Serhiy Storchacha in bpo-16486.)
The writeframesraw()
and writeframes()
methods now accept any bytes-like object. (Contributed by Serhiy
Storchaka in bpo-8311.)
argparse¶
The FileType
class now accepts encoding and
errors arguments, which are passed through to open()
. (Contributed
by Lucas Maystre in bpo-11175.)
audioop¶
audioop
now supports 24-bit samples. (Contributed by Serhiy Storchaka
in bpo-12866.)
New byteswap()
function converts big-endian samples to
little-endian and vice versa. (Contributed by Serhiy Storchaka in
bpo-19641.)
All audioop
functions now accept any bytes-like object. Strings
are not accepted: they didn’t work before, now they raise an error right away.
(Contributed by Serhiy Storchaka in bpo-16685.)
base64¶
The encoding and decoding functions in base64
now accept any
bytes-like object in cases where it previously required a
bytes
or bytearray
instance. (Contributed by Nick Coghlan in
bpo-17839.)
New functions a85encode()
, a85decode()
,
b85encode()
, and b85decode()
provide the ability to
encode and decode binary data from and to Ascii85
and the git/mercurial
Base85
formats, respectively. The a85
functions have options that can
be used to make them compatible with the variants of the Ascii85
encoding,
including the Adobe variant. (Contributed by Martin Morrison, the Mercurial
project, Serhiy Storchaka, and Antoine Pitrou in bpo-17618.)
collections¶
The ChainMap.new_child()
method now accepts an m argument specifying
the child map to add to the chain. This allows an existing mapping and/or a
custom mapping type to be used for the child. (Contributed by Vinay Sajip in
bpo-16613.)
colorsys¶
The number of digits in the coefficients for the RGB — YIQ conversions have been expanded so that they match the FCC NTSC versions. The change in results should be less than 1% and may better match results found elsewhere. (Contributed by Brian Landers and Serhiy Storchaka in bpo-14323.)
contextlib¶
The new contextlib.suppress
context manager helps to clarify the
intent of code that deliberately suppresses exceptions from a single
statement. (Contributed by Raymond Hettinger in bpo-15806 and
Zero Piraeus in bpo-19266.)
The new contextlib.redirect_stdout()
context manager makes it easier
for utility scripts to handle inflexible APIs that write their output to
sys.stdout
and don’t provide any options to redirect it. Using the
context manager, the sys.stdout
output can be redirected to any
other stream or, in conjunction with io.StringIO
, to a string.
The latter can be especially useful, for example, to capture output
from a function that was written to implement a command line interface.
It is recommended only for utility scripts because it affects the
global state of sys.stdout
. (Contributed by Raymond Hettinger
in bpo-15805.)
The contextlib
documentation has also been updated to include a
discussion of the
differences between single use, reusable and reentrant context managers.
dbm¶
dbm.open()
objects now support the context management protocol. When
used in a with
statement, the close
method of the database
object will be called automatically at the end of the block. (Contributed by
Claudiu Popa and Nick Coghlan in bpo-19282.)
dis¶
Functions show_code()
, dis()
, distb()
, and
disassemble()
now accept a keyword-only file argument that
controls where they write their output.
The dis
module is now built around an Instruction
class
that provides object oriented access to the details of each individual bytecode
operation.
A new method, get_instructions()
, provides an iterator that emits
the Instruction stream for a given piece of Python code. Thus it is now
possible to write a program that inspects and manipulates a bytecode
object in ways different from those provided by the dis
module
itself. For example:
>>> import dis
>>> for instr in dis.get_instructions(lambda x: x + 1):
... print(instr.opname)
LOAD_FAST
LOAD_CONST
BINARY_ADD
RETURN_VALUE
The various display tools in the dis
module have been rewritten to use
these new components.
In addition, a new application-friendly class Bytecode
provides
an object-oriented API for inspecting bytecode in both in human-readable form
and for iterating over instructions. The Bytecode
constructor
takes the same arguments that get_instructions()
does (plus an
optional current_offset), and the resulting object can be iterated to produce
Instruction
objects. But it also has a dis
method, equivalent to calling dis
on the constructor argument, but
returned as a multi-line string:
>>> bytecode = dis.Bytecode(lambda x: x + 1, current_offset=3)
>>> for instr in bytecode:
... print('{} ({})'.format(instr.opname, instr.opcode))
LOAD_FAST (124)
LOAD_CONST (100)
BINARY_ADD (23)
RETURN_VALUE (83)
>>> bytecode.dis().splitlines()
[' 1 0 LOAD_FAST 0 (x)',
' --> 3 LOAD_CONST 1 (1)',
' 6 BINARY_ADD',
' 7 RETURN_VALUE']
Bytecode
also has a class method,
from_traceback()
, that provides the ability to manipulate a
traceback (that is, print(Bytecode.from_traceback(tb).dis())
is equivalent
to distb(tb)
).
(Contributed by Nick Coghlan, Ryan Kelly and Thomas Kluyver in bpo-11816 and Claudiu Popa in bpo-17916.)
New function stack_effect()
computes the effect on the Python stack
of a given opcode and argument, information that is not otherwise available.
(Contributed by Larry Hastings in bpo-19722.)
doctest¶
A new option flag, FAIL_FAST
, halts
test running as soon as the first failure is detected. (Contributed by R.
David Murray and Daniel Urban in bpo-16522.)
The doctest
command line interface now uses argparse
, and has two
new options, -o
and -f
. -o
allows doctest options to be specified on the command line, and -f
is a
shorthand for -o FAIL_FAST
(to parallel the similar option supported by the
unittest
CLI). (Contributed by R. David Murray in bpo-11390.)
doctest
will now find doctests in extension module __doc__
strings.
(Contributed by Zachary Ware in bpo-3158.)
email¶
as_string()
now accepts a policy argument to
override the default policy of the message when generating a string
representation of it. This means that as_string
can now be used in more
circumstances, instead of having to create and use a generator
in
order to pass formatting parameters to its flatten
method. (Contributed by
R. David Murray in bpo-18600.)
New method as_bytes()
added to produce a bytes
representation of the message in a fashion similar to how as_string
produces a string representation. It does not accept the maxheaderlen
argument, but does accept the unixfrom and policy arguments. The
Message
__bytes__()
method
calls it, meaning that bytes(mymsg)
will now produce the intuitive
result: a bytes object containing the fully formatted message. (Contributed
by R. David Murray in bpo-18600.)
The Message.set_param()
message now accepts a replace keyword argument.
When specified, the associated header will be updated without changing
its location in the list of headers. For backward compatibility, the default
is False
. (Contributed by R. David Murray in bpo-18891.)
A pair of new subclasses of Message
have been added
(EmailMessage
and MIMEPart
), along with a new sub-module,
contentmanager
and a new policy
attribute
content_manager
. All documentation is
currently in the new module, which is being added as part of email’s new
provisional API. These classes provide a number of new methods that
make extracting content from and inserting content into email messages much
easier. For details, see the contentmanager
documentation and
the email: Examples. These API additions complete the
bulk of the work that was planned as part of the email6 project. The currently
provisional API is scheduled to become final in Python 3.5 (possibly with a few
minor additions in the area of error handling). (Contributed by R. David
Murray in bpo-18891.)
filecmp¶
A new clear_cache()
function provides the ability to clear the
filecmp
comparison cache, which uses os.stat()
information to
determine if the file has changed since the last compare. This can be used,
for example, if the file might have been changed and re-checked in less time
than the resolution of a particular filesystem’s file modification time field.
(Contributed by Mark Levitt in bpo-18149.)
New module attribute DEFAULT_IGNORES
provides the list of
directories that are used as the default value for the ignore parameter of
the dircmp()
function. (Contributed by Eli Bendersky in
bpo-15442.)
functools¶
The new partialmethod()
descriptor brings partial argument
application to descriptors, just as partial()
provides
for normal callables. The new descriptor also makes it easier to get
arbitrary callables (including partial()
instances)
to behave like normal instance methods when included in a class definition.
(Contributed by Alon Horev and Nick Coghlan in bpo-4331.)
The new singledispatch()
decorator brings support for
single-dispatch generic functions to the Python standard library. Where
object oriented programming focuses on grouping multiple operations on a
common set of data into a class, a generic function focuses on grouping
multiple implementations of an operation that allows it to work with
different kinds of data.
See also
- PEP 443 – Single-dispatch generic functions
PEP written and implemented by Łukasz Langa.
total_ordering()
now supports a return value of
NotImplemented
from the underlying comparison function. (Contributed
by Katie Miller in bpo-10042.)
A pure-python version of the partial()
function is now in the
stdlib; in CPython it is overridden by the C accelerated version, but it is
available for other implementations to use. (Contributed by Brian Thorne in
bpo-12428.)
gc¶
New function get_stats()
returns a list of three per-generation
dictionaries containing the collections statistics since interpreter startup.
(Contributed by Antoine Pitrou in bpo-16351.)
glob¶
A new function escape()
provides a way to escape special characters
in a filename so that they do not become part of the globbing expansion but are
instead matched literally. (Contributed by Serhiy Storchaka in bpo-8402.)
hashlib¶
A new hashlib.pbkdf2_hmac()
function provides
the PKCS#5 password-based key derivation function 2. (Contributed by Christian
Heimes in bpo-18582.)
The name
attribute of hashlib
hash objects is now
a formally supported interface. It has always existed in CPython’s
hashlib
(although it did not return lower case names for all supported
hashes), but it was not a public interface and so some other Python
implementations have not previously supported it. (Contributed by Jason R.
Coombs in bpo-18532.)
hmac¶
hmac
now accepts bytearray
as well as bytes
for the key
argument to the new()
function, and the msg parameter to both the
new()
function and the update()
method now
accepts any type supported by the hashlib
module. (Contributed
by Jonas Borgström in bpo-18240.)
The digestmod argument to the hmac.new()
function may now be any hash
digest name recognized by hashlib
. In addition, the current behavior in
which the value of digestmod defaults to MD5
is deprecated: in a
future version of Python there will be no default value. (Contributed by
Christian Heimes in bpo-17276.)
With the addition of block_size
and name
attributes (and the formal documentation of the digest_size
attribute), the hmac
module now conforms fully to the PEP 247 API.
(Contributed by Christian Heimes in bpo-18775.)
html¶
New function unescape()
function converts HTML5 character references to
the corresponding Unicode characters. (Contributed by Ezio Melotti in
bpo-2927.)
HTMLParser
accepts a new keyword argument
convert_charrefs that, when True
, automatically converts all character
references. For backward-compatibility, its value defaults to False
, but
it will change to True
in a future version of Python, so you are invited to
set it explicitly and update your code to use this new feature. (Contributed
by Ezio Melotti in bpo-13633.)
The strict argument of HTMLParser
is now deprecated.
(Contributed by Ezio Melotti in bpo-15114.)
http¶
send_error()
now accepts an
optional additional explain parameter which can be used to provide an
extended error description, overriding the hardcoded default if there is one.
This extended error description will be formatted using the
error_message_format
attribute
and sent as the body of the error response.
(Contributed by Karl Cow in bpo-12921.)
The http.server
command line interface now has
a -b/--bind
option that causes the server to listen on a specific address.
(Contributed by Malte Swart in bpo-17764.)
idlelib and IDLE¶
Since idlelib implements the IDLE shell and editor and is not intended for
import by other programs, it gets improvements with every release. See
Lib/idlelib/NEWS.txt
for a cumulative list of changes since 3.3.0,
as well as changes made in future 3.4.x releases. This file is also available
from the IDLE dialog.
importlib¶
The InspectLoader
ABC defines a new method,
source_to_code()
that accepts source
data and a path and returns a code object. The default implementation
is equivalent to compile(data, path, 'exec', dont_inherit=True)
.
(Contributed by Eric Snow and Brett Cannon in bpo-15627.)
InspectLoader
also now has a default implementation
for the get_code()
method. However,
it will normally be desirable to override the default implementation
for performance reasons. (Contributed by Brett Cannon in bpo-18072.)
The reload()
function has been moved from imp
to
importlib
as part of the imp
module deprecation. (Contributed by
Berker Peksag in bpo-18193.)
importlib.util
now has a MAGIC_NUMBER
attribute
providing access to the bytecode version number. This replaces the
get_magic()
function in the deprecated imp
module.
(Contributed by Brett Cannon in bpo-18192.)
New importlib.util
functions cache_from_source()
and source_from_cache()
replace the same-named functions
in the deprecated imp
module. (Contributed by Brett Cannon in
bpo-18194.)
The importlib
bootstrap NamespaceLoader
now conforms to
the InspectLoader
ABC, which means that runpy
and
python -m
can now be used with namespace packages. (Contributed
by Brett Cannon in bpo-18058.)
importlib.util
has a new function decode_source()
that decodes source from bytes using universal newline processing. This is
useful for implementing InspectLoader.get_source()
methods.
importlib.machinery.ExtensionFileLoader
now has a
get_filename()
method. This was
inadvertently omitted in the original implementation. (Contributed by Eric
Snow in bpo-19152.)
inspect¶
The inspect
module now offers a basic command line interface to quickly display source code and other
information for modules, classes and functions. (Contributed by Claudiu Popa
and Nick Coghlan in bpo-18626.)
unwrap()
makes it easy to unravel wrapper function chains
created by functools.wraps()
(and any other API that sets the
__wrapped__
attribute on a wrapper function). (Contributed by
Daniel Urban, Aaron Iles and Nick Coghlan in bpo-13266.)
As part of the implementation of the new enum
module, the
inspect
module now has substantially better support for custom
__dir__
methods and dynamic class attributes provided through
metaclasses. (Contributed by Ethan Furman in bpo-18929 and
bpo-19030.)
getfullargspec()
and getargspec()
now use the signature()
API. This allows them to
support a much broader range of callables, including those with
__signature__
attributes, those with metadata provided by argument
clinic, functools.partial()
objects and more. Note that, unlike
signature()
, these functions still ignore __wrapped__
attributes, and report the already bound first argument for bound methods,
so it is still necessary to update your code to use
signature()
directly if those features are desired.
(Contributed by Yury Selivanov in bpo-17481.)
signature()
now supports duck types of CPython functions,
which adds support for functions compiled with Cython. (Contributed
by Stefan Behnel and Yury Selivanov in bpo-17159.)
ipaddress¶
ipaddress
was added to the standard library in Python 3.3 as a
provisional API. With the release of Python 3.4, this qualification
has been removed: ipaddress
is now considered a stable API, covered
by the normal standard library requirements to maintain backwards
compatibility.
A new is_global
property is True
if
an address is globally routeable. (Contributed by Peter Moody in
bpo-17400.)
logging¶
The TimedRotatingFileHandler
has a new atTime
parameter that can be used to specify the time of day when rollover should
happen. (Contributed by Ronald Oussoren in bpo-9556.)
SocketHandler
and
DatagramHandler
now support Unix domain sockets (by
setting port to None
). (Contributed by Vinay Sajip in commit
ce46195b56a9.)
fileConfig()
now accepts a
configparser.RawConfigParser
subclass instance for the fname
parameter. This facilitates using a configuration file when logging
configuration is just a part of the overall application configuration, or where
the application modifies the configuration before passing it to
fileConfig()
. (Contributed by Vinay Sajip in
bpo-16110.)
Logging configuration data received from a socket via the
logging.config.listen()
function can now be validated before being
processed by supplying a verification function as the argument to the new
verify keyword argument. (Contributed by Vinay Sajip in bpo-15452.)
marshal¶
The default marshal
version has been bumped to 3. The code implementing
the new version restores the Python2 behavior of recording only one copy of
interned strings and preserving the interning on deserialization, and extends
this “one copy” ability to any object type (including handling recursive
references). This reduces both the size of .pyc
files and the amount of
memory a module occupies in memory when it is loaded from a .pyc
(or
.pyo
) file. (Contributed by Kristján Valur Jónsson in bpo-16475,
with additional speedups by Antoine Pitrou in bpo-19219.)
mmap¶
mmap objects are now weakly referenceable. (Contributed by Valerie Lambert in bpo-4885.)
multiprocessing¶
On Unix two new start methods,
spawn
and forkserver
, have been added for starting processes using
multiprocessing
. These make the mixing of processes with threads more
robust, and the spawn
method matches the semantics that multiprocessing has
always used on Windows. New function
get_all_start_methods()
reports all start methods
available on the platform, get_start_method()
reports
the current start method, and set_start_method()
sets
the start method. (Contributed by Richard Oudkerk in bpo-8713.)
multiprocessing
also now has the concept of a context
, which
determines how child processes are created. New function
get_context()
returns a context that uses a specified
start method. It has the same API as the multiprocessing
module itself,
so you can use it to create Pool
s and other
objects that will operate within that context. This allows a framework and an
application or different parts of the same application to use multiprocessing
without interfering with each other. (Contributed by Richard Oudkerk in
bpo-18999.)
Except when using the old fork start method, child processes no longer inherit unneeded handles/file descriptors from their parents (part of bpo-8713).
multiprocessing
now relies on runpy
(which implements the
-m
switch) to initialise __main__
appropriately in child processes
when using the spawn
or forkserver
start methods. This resolves some
edge cases where combining multiprocessing, the -m
command line switch,
and explicit relative imports could cause obscure failures in child
processes. (Contributed by Nick Coghlan in bpo-19946.)
operator¶
New function length_hint()
provides an implementation of the
specification for how the __length_hint__()
special method should
be used, as part of the PEP 424 formal specification of this language
feature. (Contributed by Armin Ronacher in bpo-16148.)
There is now a pure-python version of the operator
module available for
reference and for use by alternate implementations of Python. (Contributed by
Zachary Ware in bpo-16694.)
os¶
There are new functions to get and set the inheritable flag of a file descriptor (os.get_inheritable()
,
os.set_inheritable()
) or a Windows handle
(os.get_handle_inheritable()
, os.set_handle_inheritable()
).
New function cpu_count()
reports the number of CPUs available on the
platform on which Python is running (or None
if the count can’t be
determined). The multiprocessing.cpu_count()
function is now implemented
in terms of this function). (Contributed by Trent Nelson, Yogesh Chaudhari,
Victor Stinner, and Charles-François Natali in bpo-17914.)
os.path.samestat()
is now available on the Windows platform (and the
os.path.samefile()
implementation is now shared between Unix and
Windows). (Contributed by Brian Curtin in bpo-11939.)
os.path.ismount()
now recognizes volumes mounted below a drive
root on Windows. (Contributed by Tim Golden in bpo-9035.)
os.open()
supports two new flags on platforms that provide them,
O_PATH
(un-opened file descriptor), and O_TMPFILE
(unnamed temporary file; as of 3.4.0 release available only on Linux systems
with a kernel version of 3.11 or newer that have uapi headers). (Contributed
by Christian Heimes in bpo-18673 and Benjamin Peterson, respectively.)
pdb¶
pdb
has been enhanced to handle generators, yield
, and
yield from
in a more useful fashion. This is especially helpful when
debugging asyncio
based programs. (Contributed by Andrew Svetlov and
Xavier de Gaye in bpo-16596.)
The print
command has been removed from pdb
, restoring access to the
Python print()
function from the pdb command line. Python2’s pdb
did
not have a print
command; instead, entering print
executed the
print
statement. In Python3 print
was mistakenly made an alias for the
pdb p
command. p
, however, prints the repr
of its argument,
not the str
like the Python2 print
command did. Worse, the Python3
pdb print
command shadowed the Python3 print
function, making it
inaccessible at the pdb
prompt. (Contributed by Connor Osborn in
bpo-18764.)
pickle¶
pickle
now supports (but does not use by default) a new pickle protocol,
protocol 4. This new protocol addresses a number of issues that were present
in previous protocols, such as the serialization of nested classes, very large
strings and containers, and classes whose __new__()
method takes
keyword-only arguments. It also provides some efficiency improvements.
See also
- PEP 3154 – Pickle protocol 4
PEP written by Antoine Pitrou and implemented by Alexandre Vassalotti.
plistlib¶
plistlib
now has an API that is similar to the standard pattern for
stdlib serialization protocols, with new load()
,
dump()
, loads()
, and dumps()
functions. (The older API is now deprecated.) In addition to the already
supported XML plist format (FMT_XML
), it also now supports
the binary plist format (FMT_BINARY
). (Contributed by Ronald
Oussoren and others in bpo-14455.)
poplib¶
Two new methods have been added to poplib
: capa()
,
which returns the list of capabilities advertised by the POP server, and
stls()
, which switches a clear-text POP3 session into an
encrypted POP3 session if the POP server supports it. (Contributed by Lorenzo
Catucci in bpo-4473.)
pprint¶
The pprint
module’s PrettyPrinter
class and its
pformat()
, and pprint()
functions have a new
option, compact, that controls how the output is formatted. Currently
setting compact to True
means that sequences will be printed with as many
sequence elements as will fit within width on each (indented) line.
(Contributed by Serhiy Storchaka in bpo-19132.)
Long strings are now wrapped using Python’s normal line continuation syntax. (Contributed by Antoine Pitrou in bpo-17150.)
pty¶
pty.spawn()
now returns the status value from os.waitpid()
on
the child process, instead of None
. (Contributed by Gregory P. Smith.)
pydoc¶
The pydoc
module is now based directly on the inspect.signature()
introspection API, allowing it to provide signature information for a wider
variety of callable objects. This change also means that __wrapped__
attributes are now taken into account when displaying help information.
(Contributed by Larry Hastings in bpo-19674.)
The pydoc
module no longer displays the self
parameter for
already bound methods. Instead, it aims to always display the exact current
signature of the supplied callable. (Contributed by Larry Hastings in
bpo-20710.)
In addition to the changes that have been made to pydoc
directly,
its handling of custom __dir__
methods and various descriptor
behaviours has also been improved substantially by the underlying changes in
the inspect
module.
As the help()
builtin is based on pydoc
, the above changes also
affect the behaviour of help()
.
re¶
New fullmatch()
function and Pattern.fullmatch()
method anchor
the pattern at both ends of the string to match. This provides a way to be
explicit about the goal of the match, which avoids a class of subtle bugs where
$
characters get lost during code changes or the addition of alternatives
to an existing regular expression. (Contributed by Matthew Barnett in
bpo-16203.)
The repr of regex objects now includes the pattern and the flags; the repr of match objects now includes the start, end, and the part of the string that matched. (Contributed by Hugo Lopes Tavares and Serhiy Storchaka in bpo-13592 and bpo-17087.)
resource¶
New prlimit()
function, available on Linux platforms with a
kernel version of 2.6.36 or later and glibc of 2.13 or later, provides the
ability to query or set the resource limits for processes other than the one
making the call. (Contributed by Christian Heimes in bpo-16595.)
On Linux kernel version 2.6.36 or later, there are also some new
Linux specific constants: RLIMIT_MSGQUEUE
,
RLIMIT_NICE
, RLIMIT_RTPRIO
,
RLIMIT_RTTIME
, and RLIMIT_SIGPENDING
.
(Contributed by Christian Heimes in bpo-19324.)
On FreeBSD version 9 and later, there some new FreeBSD specific constants:
RLIMIT_SBSIZE
, RLIMIT_SWAP
, and
RLIMIT_NPTS
. (Contributed by Claudiu Popa in
bpo-19343.)
select¶
epoll
objects now support the context management protocol.
When used in a with
statement, the close()
method will be called automatically at the end of the block. (Contributed
by Serhiy Storchaka in bpo-16488.)
devpoll
objects now have fileno()
and
close()
methods, as well as a new attribute
closed
. (Contributed by Victor Stinner in
bpo-18794.)
shelve¶
Shelf
instances may now be used in with
statements,
and will be automatically closed at the end of the with
block.
(Contributed by Filip Gruszczyński in bpo-13896.)
shutil¶
copyfile()
now raises a specific Error
subclass,
SameFileError
, when the source and destination are the same
file, which allows an application to take appropriate action on this specific
error. (Contributed by Atsuo Ishimoto and Hynek Schlawack in
bpo-1492704.)
smtpd¶
The SMTPServer
and SMTPChannel
classes now
accept a map keyword argument which, if specified, is passed in to
asynchat.async_chat
as its map argument. This allows an application
to avoid affecting the global socket map. (Contributed by Vinay Sajip in
bpo-11959.)
smtplib¶
SMTPException
is now a subclass of OSError
, which allows
both socket level errors and SMTP protocol level errors to be caught in one
try/except statement by code that only cares whether or not an error occurred.
(Contributed by Ned Jackson Lovely in bpo-2118.)
socket¶
The socket module now supports the CAN_BCM
protocol on
platforms that support it. (Contributed by Brian Thorne in bpo-15359.)
Socket objects have new methods to get or set their inheritable flag, get_inheritable()
and
set_inheritable()
.
The socket.AF_*
and socket.SOCK_*
constants are now enumeration values
using the new enum
module. This allows meaningful names to be printed
during debugging, instead of integer “magic numbers”.
The AF_LINK
constant is now available on BSD and OSX.
inet_pton()
and inet_ntop()
are now supported
on Windows. (Contributed by Atsuo Ishimoto in bpo-7171.)
sqlite3¶
A new boolean parameter to the connect()
function, uri, can be
used to indicate that the database parameter is a uri
(see the SQLite
URI documentation). (Contributed by poq in
bpo-13773.)
ssl¶
PROTOCOL_TLSv1_1
and PROTOCOL_TLSv1_2
(TLSv1.1 and
TLSv1.2 support) have been added; support for these protocols is only available if
Python is linked with OpenSSL 1.0.1 or later. (Contributed by Michele Orrù and
Antoine Pitrou in bpo-16692.)
New function create_default_context()
provides a standard way to
obtain an SSLContext
whose settings are intended to be a
reasonable balance between compatibility and security. These settings are
more stringent than the defaults provided by the SSLContext
constructor, and may be adjusted in the future, without prior deprecation, if
best-practice security requirements change. The new recommended best
practice for using stdlib libraries that support SSL is to use
create_default_context()
to obtain an SSLContext
object, modify it if needed, and then pass it as the context argument
of the appropriate stdlib API. (Contributed by Christian Heimes
in bpo-19689.)
SSLContext
method load_verify_locations()
accepts a new optional argument cadata, which can be used to provide PEM or
DER encoded certificates directly via strings or bytes, respectively.
(Contributed by Christian Heimes in bpo-18138.)
New function get_default_verify_paths()
returns
a named tuple of the paths and environment variables that the
set_default_verify_paths()
method uses to set
OpenSSL’s default cafile
and capath
. This can be an aid in
debugging default verification issues. (Contributed by Christian Heimes
in bpo-18143.)
SSLContext
has a new method,
cert_store_stats()
, that reports the number of loaded
X.509
certs, X.509 CA
certs, and certificate revocation lists
(crl
s), as well as a get_ca_certs()
method that
returns a list of the loaded CA
certificates. (Contributed by Christian
Heimes in bpo-18147.)
If OpenSSL 0.9.8 or later is available, SSLContext
has a new
attribute verify_flags
that can be used to control the
certificate verification process by setting it to some combination of the new
constants VERIFY_DEFAULT
, VERIFY_CRL_CHECK_LEAF
,
VERIFY_CRL_CHECK_CHAIN
, or VERIFY_X509_STRICT
.
OpenSSL does not do any CRL verification by default. (Contributed by
Christien Heimes in bpo-8813.)
New SSLContext
method load_default_certs()
loads a set of default “certificate authority” (CA) certificates from default
locations, which vary according to the platform. It can be used to load both
TLS web server authentication certificates
(purpose=
SERVER_AUTH
) for a client to use to verify a
server, and certificates for a server to use in verifying client certificates
(purpose=
CLIENT_AUTH
). (Contributed by Christian
Heimes in bpo-19292.)
Two new windows-only functions, enum_certificates()
and
enum_crls()
provide the ability to retrieve certificates,
certificate information, and CRLs from the Windows cert store. (Contributed
by Christian Heimes in bpo-17134.)
Support for server-side SNI (Server Name Indication) using the new
ssl.SSLContext.set_servername_callback()
method.
(Contributed by Daniel Black in bpo-8109.)
The dictionary returned by SSLSocket.getpeercert()
contains additional
X509v3
extension items: crlDistributionPoints
, calIssuers
, and
OCSP
URIs. (Contributed by Christian Heimes in bpo-18379.)
stat¶
The stat
module is now backed by a C implementation in _stat
. A C
implementation is required as most of the values aren’t standardized and
are platform-dependent. (Contributed by Christian Heimes in bpo-11016.)
The module supports new ST_MODE
flags, S_IFDOOR
,
S_IFPORT
, and S_IFWHT
. (Contributed by
Christian Hiemes in bpo-11016.)
struct¶
New function iter_unpack
and a new
struct.Struct.iter_unpack()
method on compiled formats provide streamed
unpacking of a buffer containing repeated instances of a given format of data.
(Contributed by Antoine Pitrou in bpo-17804.)
subprocess¶
check_output()
now accepts an input argument that can
be used to provide the contents of stdin
for the command that is run.
(Contributed by Zack Weinberg in bpo-16624.)
getoutput()
and getstatusoutput()
now
work on Windows. This change was actually inadvertently made in 3.3.4.
(Contributed by Tim Golden in bpo-10197.)
sunau¶
The getparams()
method now returns a namedtuple rather than a
plain tuple. (Contributed by Claudiu Popa in bpo-18901.)
sunau.open()
now supports the context management protocol: when used in a
with
block, the close
method of the returned object will be
called automatically at the end of the block. (Contributed by Serhiy Storchaka
in bpo-18878.)
AU_write.setsampwidth()
now supports 24 bit samples, thus adding
support for writing 24 sample using the module. (Contributed by
Serhiy Storchaka in bpo-19261.)
The writeframesraw()
and
writeframes()
methods now accept any bytes-like
object. (Contributed by Serhiy Storchaka in bpo-8311.)
sys¶
New function sys.getallocatedblocks()
returns the current number of
blocks allocated by the interpreter. (In CPython with the default
--with-pymalloc
setting, this is allocations made through the
PyObject_Malloc()
API.) This can be useful for tracking memory leaks,
especially if automated via a test suite. (Contributed by Antoine Pitrou
in bpo-13390.)
When the Python interpreter starts in interactive mode, it checks for an __interactivehook__
attribute
on the sys
module. If the attribute exists, its value is called with no
arguments just before interactive mode is started. The check is made after the
PYTHONSTARTUP
file is read, so it can be set there. The site
module sets it to a function that enables tab
completion and history saving (in ~/.python-history
) if the platform
supports readline
. If you do not want this (new) behavior, you can
override it in PYTHONSTARTUP
, sitecustomize
, or
usercustomize
by deleting this attribute from sys
(or setting it
to some other callable). (Contributed by Éric Araujo and Antoine Pitrou in
bpo-5845.)
tarfile¶
The tarfile
module now supports a simple Command-Line Interface when
called as a script directly or via -m
. This can be used to create and
extract tarfile archives. (Contributed by Berker Peksag in bpo-13477.)
textwrap¶
The TextWrapper
class has two new attributes/constructor
arguments: max_lines
, which limits the number of
lines in the output, and placeholder
, which is a
string that will appear at the end of the output if it has been truncated
because of max_lines. Building on these capabilities, a new convenience
function shorten()
collapses all of the whitespace in the input
to single spaces and produces a single line of a given width that ends with
the placeholder (by default, [...]
). (Contributed by Antoine Pitrou and
Serhiy Storchaka in bpo-18585 and bpo-18725.)
threading¶
The Thread
object representing the main thread can be
obtained from the new main_thread()
function. In normal
conditions this will be the thread from which the Python interpreter was
started. (Contributed by Andrew Svetlov in bpo-18882.)
traceback¶
A new traceback.clear_frames()
function takes a traceback object
and clears the local variables in all of the frames it references,
reducing the amount of memory consumed. (Contributed by Andrew Kuchling in
bpo-1565525.)
types¶
A new DynamicClassAttribute()
descriptor provides a way to define
an attribute that acts normally when looked up through an instance object, but
which is routed to the class __getattr__
when looked up through the
class. This allows one to have properties active on a class, and have virtual
attributes on the class with the same name (see enum
for an example).
(Contributed by Ethan Furman in bpo-19030.)
urllib¶
urllib.request
now supports data:
URLs via the
DataHandler
class. (Contributed by Mathias Panzenböck
in bpo-16423.)
The http method that will be used by a Request
class
can now be specified by setting a method
class attribute on the subclass. (Contributed by Jason R Coombs in
bpo-18978.)
Request
objects are now reusable: if the
full_url
or data
attributes are modified, all relevant internal properties are updated. This
means, for example, that it is now possible to use the same
Request
object in more than one
OpenerDirector.open()
call with different data arguments, or to
modify a Request
‘s url
rather than recomputing it
from scratch. There is also a new
remove_header()
method that can be used to remove
headers from a Request
. (Contributed by Alexey
Kachayev in bpo-16464, Daniel Wozniak in bpo-17485, and Damien Brecht
and Senthil Kumaran in bpo-17272.)
HTTPError
objects now have a
headers
attribute that provides access to the
HTTP response headers associated with the error. (Contributed by
Berker Peksag in bpo-15701.)
unittest¶
The TestCase
class has a new method,
subTest()
, that produces a context manager whose
with
block becomes a “sub-test”. This context manager allows a test
method to dynamically generate subtests by, say, calling the subTest
context manager inside a loop. A single test method can thereby produce an
indefinite number of separately identified and separately counted tests, all of
which will run even if one or more of them fail. For example:
class NumbersTest(unittest.TestCase):
def test_even(self):
for i in range(6):
with self.subTest(i=i):
self.assertEqual(i % 2, 0)
will result in six subtests, each identified in the unittest verbose output
with a label consisting of the variable name i
and a particular value for
that variable (i=0
, i=1
, etc). See Distinguishing test iterations using subtests for the full
version of this example. (Contributed by Antoine Pitrou in bpo-16997.)
unittest.main()
now accepts an iterable of test names for
defaultTest, where previously it only accepted a single test name as a
string. (Contributed by Jyrki Pulliainen in bpo-15132.)
If SkipTest
is raised during test discovery (that is, at the
module level in the test file), it is now reported as a skip instead of an
error. (Contributed by Zach Ware in bpo-16935.)
discover()
now sorts the discovered files to provide
consistent test ordering. (Contributed by Martin Melin and Jeff Ramnani in
bpo-16709.)
TestSuite
now drops references to tests as soon as the test
has been run, if the test is successful. On Python interpreters that do
garbage collection, this allows the tests to be garbage collected if nothing
else is holding a reference to the test. It is possible to override this
behavior by creating a TestSuite
subclass that defines a
custom _removeTestAtIndex
method. (Contributed by Tom Wardill, Matt
McClure, and Andrew Svetlov in bpo-11798.)
A new test assertion context-manager, assertLogs()
,
will ensure that a given block of code emits a log message using the
logging
module. By default the message can come from any logger and
have a priority of INFO
or higher, but both the logger name and an
alternative minimum logging level may be specified. The object returned by the
context manager can be queried for the LogRecord
s and/or
formatted messages that were logged. (Contributed by Antoine Pitrou in
bpo-18937.)
Test discovery now works with namespace packages (Contributed by Claudiu Popa in bpo-17457.)
unittest.mock
objects now inspect their specification signatures when
matching calls, which means an argument can now be matched by either position
or name, instead of only by position. (Contributed by Antoine Pitrou in
bpo-17015.)
mock_open()
objects now have readline
and readlines
methods. (Contributed by Toshio Kuratomi in bpo-17467.)
venv¶
venv
now includes activation scripts for the csh
and fish
shells. (Contributed by Andrew Svetlov in bpo-15417.)
EnvBuilder
and the create()
convenience function
take a new keyword argument with_pip, which defaults to False
, that
controls whether or not EnvBuilder
ensures that pip
is
installed in the virtual environment. (Contributed by Nick Coghlan in
bpo-19552 as part of the PEP 453 implementation.)
wave¶
The getparams()
method now returns a namedtuple rather
than a plain tuple. (Contributed by Claudiu Popa in bpo-17487.)
wave.open()
now supports the context management protocol. (Contributed
by Claudiu Popa in bpo-17616.)
wave
can now write output to unseekable files. (Contributed by David Jones, Guilherme Polo, and Serhiy
Storchaka in bpo-5202.)
The writeframesraw()
and
writeframes()
methods now accept any bytes-like
object. (Contributed by Serhiy Storchaka in bpo-8311.)
weakref¶
New WeakMethod
class simulates weak references to bound
methods. (Contributed by Antoine Pitrou in bpo-14631.)
New finalize
class makes it possible to register a callback
to be invoked when an object is garbage collected, without needing to
carefully manage the lifecycle of the weak reference itself. (Contributed by
Richard Oudkerk in bpo-15528.)
The callback, if any, associated with a ref
is now
exposed via the __callback__
attribute. (Contributed
by Mark Dickinson in bpo-17643.)
xml.etree¶
A new parser, XMLPullParser
, allows a
non-blocking applications to parse XML documents. An example can be
seen at Pull API for non-blocking parsing. (Contributed by Antoine
Pitrou in bpo-17741.)
The xml.etree.ElementTree
tostring()
and
tostringlist()
functions, and the
ElementTree
write()
method, now have a
short_empty_elements keyword-only parameter
providing control over whether elements with no content are written in
abbreviated (<tag />
) or expanded (<tag></tag>
) form. (Contributed by
Ariel Poliak and Serhiy Storchaka in bpo-14377.)
zipfile¶
The writepy()
method of the
PyZipFile
class has a new filterfunc option that can be
used to control which directories and files are added to the archive. For
example, this could be used to exclude test files from the archive.
(Contributed by Christian Tismer in bpo-19274.)
The allowZip64 parameter to ZipFile
and
PyZipFile
is now True
by default. (Contributed by
William Mallard in bpo-17201.)
CPython Implementation Changes¶
PEP 445: Customization of CPython Memory Allocators¶
PEP 445 adds new C level interfaces to customize memory allocation in the CPython interpreter.
See also
- PEP 445 – Add new APIs to customize Python memory allocators
PEP written and implemented by Victor Stinner.
PEP 442: Safe Object Finalization¶
PEP 442 removes the current limitations and quirks of object finalization
in CPython. With it, objects with __del__()
methods, as well as
generators with finally
clauses, can be finalized when they are
part of a reference cycle.
As part of this change, module globals are no longer forcibly set to
None
during interpreter shutdown in most cases, instead relying
on the normal operation of the cyclic garbage collector. This avoids a
whole class of interpreter-shutdown-time errors, usually involving
__del__
methods, that have plagued Python since the cyclic GC
was first introduced.
See also
- PEP 442 – Safe object finalization
PEP written and implemented by Antoine Pitrou.
PEP 456: Secure and Interchangeable Hash Algorithm¶
PEP 456 follows up on earlier security fix work done on Python’s hash algorithm to address certain DOS attacks to which public facing APIs backed by dictionary lookups may be subject. (See bpo-14621 for the start of the current round of improvements.) The PEP unifies CPython’s hash code to make it easier for a packager to substitute a different hash algorithm, and switches Python’s default implementation to a SipHash implementation on platforms that have a 64 bit data type. Any performance differences in comparison with the older FNV algorithm are trivial.
The PEP adds additional fields to the sys.hash_info
named tuple to
describe the hash algorithm in use by the currently executing binary. Otherwise,
the PEP does not alter any existing CPython APIs.
PEP 436: Argument Clinic¶
“Argument Clinic” (PEP 436) is now part of the CPython build process and can be used to simplify the process of defining and maintaining accurate signatures for builtins and standard library extension modules implemented in C.
Some standard library extension modules have been converted to use Argument
Clinic in Python 3.4, and pydoc
and inspect
have been updated
accordingly.
It is expected that signature metadata for programmatic introspection will be added to additional callables implemented in C as part of Python 3.4 maintenance releases.
Note
The Argument Clinic PEP is not fully up to date with the state of the implementation. This has been deemed acceptable by the release manager and core development team in this case, as Argument Clinic will not be made available as a public API for third party use in Python 3.4.
See also
- PEP 436 – The Argument Clinic DSL
PEP written and implemented by Larry Hastings.
Other Build and C API Changes¶
The new
PyType_GetSlot()
function has been added to the stable ABI, allowing retrieval of function pointers from named type slots when using the limited API. (Contributed by Martin von Löwis in bpo-17162.)The new
Py_SetStandardStreamEncoding()
pre-initialization API allows applications embedding the CPython interpreter to reliably force a particular encoding and error handler for the standard streams. (Contributed by Bastien Montagne and Nick Coghlan in bpo-16129.)Most Python C APIs that don’t mutate string arguments are now correctly marked as accepting
const char *
rather thanchar *
. (Contributed by Serhiy Storchaka in bpo-1772673.)A new shell version of
python-config
can be used even when a python interpreter is not available (for example, in cross compilation scenarios).PyUnicode_FromFormat()
now supports width and precision specifications for%s
,%A
,%U
,%V
,%S
, and%R
. (Contributed by Ysj Ray and Victor Stinner in bpo-7330.)New function
PyStructSequence_InitType2()
supplements the existingPyStructSequence_InitType()
function. The difference is that it returns0
on success and-1
on failure.The CPython source can now be compiled using the address sanity checking features of recent versions of GCC and clang: the false alarms in the small object allocator have been silenced. (Contributed by Dhiru Kholia in bpo-18596.)
The Windows build now uses Address Space Layout Randomization and Data Execution Prevention. (Contributed by Christian Heimes in bpo-16632.)
New function
PyObject_LengthHint()
is the C API equivalent ofoperator.length_hint()
. (Contributed by Armin Ronacher in bpo-16148.)
Other Improvements¶
The python command has a new option,
-I
, which causes it to run in “isolated mode”, which means thatsys.path
contains neither the script’s directory nor the user’ssite-packages
directory, and allPYTHON*
environment variables are ignored (it implies both-s
and-E
). Other restrictions may also be applied in the future, with the goal being to isolate the execution of a script from the user’s environment. This is appropriate, for example, when Python is used to run a system script. On most POSIX systems it can and should be used in the#!
line of system scripts. (Contributed by Christian Heimes in bpo-16499.)Tab-completion is now enabled by default in the interactive interpreter on systems that support
readline
. History is also enabled by default, and is written to (and read from) the file~/.python-history
. (Contributed by Antoine Pitrou and Éric Araujo in bpo-5845.)Invoking the Python interpreter with
--version
now outputs the version to standard output instead of standard error (bpo-18338). Similar changes were made toargparse
(bpo-18920) and other modules that have script-like invocation capabilities (bpo-18922).The CPython Windows installer now adds
.py
to thePATHEXT
variable when extensions are registered, allowing users to run a python script at the windows command prompt by just typing its name without the.py
extension. (Contributed by Paul Moore in bpo-18569.)A new
make
target coverage-report will build python, run the test suite, and generate an HTML coverage report for the C codebase usinggcov
and lcov.The
-R
option to the python regression test suite now also checks for memory allocation leaks, usingsys.getallocatedblocks()
. (Contributed by Antoine Pitrou in bpo-13390.)python -m
now works with namespace packages.The
stat
module is now implemented in C, which means it gets the values for its constants from the C header files, instead of having the values hard-coded in the python module as was previously the case.Loading multiple python modules from a single OS module (
.so
,.dll
) now works correctly (previously it silently returned the first python module in the file). (Contributed by Václav Šmilauer in bpo-16421.)A new opcode,
LOAD_CLASSDEREF
, has been added to fix a bug in the loading of free variables in class bodies that could be triggered by certain uses of __prepare__. (Contributed by Benjamin Peterson in bpo-17853.)A number of MemoryError-related crashes were identified and fixed by Victor Stinner using his PEP 445-based
pyfailmalloc
tool (bpo-18408, bpo-18520).The
pyvenv
command now accepts a--copies
option to use copies rather than symlinks even on systems where symlinks are the default. (Contributed by Vinay Sajip in bpo-18807.)The
pyvenv
command also accepts a--without-pip
option to suppress the otherwise-automatic bootstrapping of pip into the virtual environment. (Contributed by Nick Coghlan in bpo-19552 as part of the PEP 453 implementation.)The encoding name is now optional in the value set for the
PYTHONIOENCODING
environment variable. This makes it possible to set just the error handler, without changing the default encoding. (Contributed by Serhiy Storchaka in bpo-18818.)The
bz2
,lzma
, andgzip
moduleopen
functions now supportx
(exclusive creation) mode. (Contributed by Tim Heaney and Vajrasky Kok in bpo-19201, bpo-19222, and bpo-19223.)
Significant Optimizations¶
The UTF-32 decoder is now 3x to 4x faster. (Contributed by Serhiy Storchaka in bpo-14625.)
The cost of hash collisions for sets is now reduced. Each hash table probe now checks a series of consecutive, adjacent key/hash pairs before continuing to make random probes through the hash table. This exploits cache locality to make collision resolution less expensive. The collision resolution scheme can be described as a hybrid of linear probing and open addressing. The number of additional linear probes defaults to nine. This can be changed at compile-time by defining LINEAR_PROBES to be any value. Set LINEAR_PROBES=0 to turn-off linear probing entirely. (Contributed by Raymond Hettinger in bpo-18771.)
The interpreter starts about 30% faster. A couple of measures lead to the speedup. The interpreter loads fewer modules on startup, e.g. the
re
,collections
andlocale
modules and their dependencies are no longer imported by default. The marshal module has been improved to load compiled Python code faster. (Contributed by Antoine Pitrou, Christian Heimes and Victor Stinner in bpo-19219, bpo-19218, bpo-19209, bpo-19205 and bpo-9548.)bz2.BZ2File
is now as fast or faster than the Python2 version for most cases.lzma.LZMAFile
has also been optimized. (Contributed by Serhiy Storchaka and Nadeem Vawda in bpo-16034.)random.getrandbits()
is 20%-40% faster for small integers (the most common use case). (Contributed by Serhiy Storchaka in bpo-16674.)By taking advantage of the new storage format for strings, pickling of strings is now significantly faster. (Contributed by Victor Stinner and Antoine Pitrou in bpo-15596.)
A performance issue in
io.FileIO.readall()
has been solved. This particularly affects Windows, and significantly speeds up the case of piping significant amounts of data throughsubprocess
. (Contributed by Richard Oudkerk in bpo-15758.)html.escape()
is now 10x faster. (Contributed by Matt Bryant in bpo-18020.)On Windows, the native
VirtualAlloc
is now used instead of the CRTmalloc
inobmalloc
. Artificial benchmarks show about a 3% memory savings.os.urandom()
now uses a lazily opened persistent file descriptor so as to avoid using many file descriptors when run in parallel from multiple threads. (Contributed by Antoine Pitrou in bpo-18756.)
Deprecated¶
This section covers various APIs and other features that have been deprecated
in Python 3.4, and will be removed in Python 3.5 or later. In most (but not
all) cases, using the deprecated APIs will produce a DeprecationWarning
when the interpreter is run with deprecation warnings enabled (for example, by
using -Wd
).
Deprecations in the Python API¶
As mentioned in PEP 451: A ModuleSpec Type for the Import System, a number of
importlib
methods and functions are deprecated:importlib.find_loader()
is replaced byimportlib.util.find_spec()
;importlib.machinery.PathFinder.find_module()
is replaced byimportlib.machinery.PathFinder.find_spec()
;importlib.abc.MetaPathFinder.find_module()
is replaced byimportlib.abc.MetaPathFinder.find_spec()
;importlib.abc.PathEntryFinder.find_loader()
andfind_module()
are replaced byimportlib.abc.PathEntryFinder.find_spec()
; all of thexxxLoader
ABCload_module
methods (importlib.abc.Loader.load_module()
,importlib.abc.InspectLoader.load_module()
,importlib.abc.FileLoader.load_module()
,importlib.abc.SourceLoader.load_module()
) should no longer be implemented, instead loaders should implement anexec_module
method (importlib.abc.Loader.exec_module()
,importlib.abc.InspectLoader.exec_module()
importlib.abc.SourceLoader.exec_module()
) and let the import system take care of the rest; andimportlib.abc.Loader.module_repr()
,importlib.util.module_for_loader()
,importlib.util.set_loader()
, andimportlib.util.set_package()
are no longer needed because their functions are now handled automatically by the import system.The
imp
module is pending deprecation. To keep compatibility with Python 2/3 code bases, the module’s removal is currently not scheduled.The
formatter
module is pending deprecation and is slated for removal in Python 3.6.MD5
as the default digestmod for thehmac.new()
function is deprecated. Python 3.6 will require an explicit digest name or constructor as digestmod argument.The internal
Netrc
class in theftplib
module has been documented as deprecated in its docstring for quite some time. It now emits aDeprecationWarning
and will be removed completely in Python 3.5.The undocumented endtime argument to
subprocess.Popen.wait()
should not have been exposed and is hopefully not in use; it is deprecated and will mostly likely be removed in Python 3.5.The strict argument of
HTMLParser
is deprecated.The
plistlib
readPlist()
,writePlist()
,readPlistFromBytes()
, andwritePlistToBytes()
functions are deprecated in favor of the corresponding new functionsload()
,dump()
,loads()
, anddumps()
.Data()
is deprecated in favor of just using thebytes
constructor.The
sysconfig
keySO
is deprecated, it has been replaced byEXT_SUFFIX
.The
U
mode accepted by variousopen
functions is deprecated. In Python3 it does not do anything useful, and should be replaced by appropriate uses ofio.TextIOWrapper
(if needed) and its newline argument.The parser argument of
xml.etree.ElementTree.iterparse()
has been deprecated, as has the html argument ofXMLParser()
. To prepare for the removal of the latter, all arguments toXMLParser
should be passed by keyword.
Deprecated Features¶
Running IDLE — Python editor and shell with the
-n
flag (no subprocess) is deprecated. However, the feature will not be removed until bpo-18823 is resolved.The site module adding a “site-python” directory to sys.path, if it exists, is deprecated (bpo-19375).
Removed¶
Operating Systems No Longer Supported¶
Support for the following operating systems has been removed from the source and build tools:
API and Feature Removals¶
The following obsolete and previously deprecated APIs and features have been removed:
The unmaintained
Misc/TextMate
andMisc/vim
directories have been removed (see the devguide for suggestions on what to use instead).The
SO
makefile macro is removed (it was replaced by theSHLIB_SUFFIX
andEXT_SUFFIX
macros) (bpo-16754).The
PyThreadState.tick_counter
field has been removed; its value has been meaningless since Python 3.2, when the “new GIL” was introduced (bpo-19199).PyLoader
andPyPycLoader
have been removed fromimportlib
. (Contributed by Taras Lyapun in bpo-15641.)The strict argument to
HTTPConnection
andHTTPSConnection
has been removed. HTTP 0.9-style “Simple Responses” are no longer supported.The deprecated
urllib.request.Request
getter and setter methodsadd_data
,has_data
,get_data
,get_type
,get_host
,get_selector
,set_proxy
,get_origin_req_host
, andis_unverifiable
have been removed (use direct attribute access instead).Support for loading the deprecated
TYPE_INT64
has been removed frommarshal
. (Contributed by Dan Riti in bpo-15480.)inspect.Signature
: positional-only parameters are now required to have a valid name.object.__format__()
no longer accepts non-empty format strings, it now raises aTypeError
instead. Using a non-empty string has been deprecated since Python 3.2. This change has been made to prevent a situation where previously working (but incorrect) code would start failing if an object gained a __format__ method, which means that your code may now raise aTypeError
if you are using an's'
format code with objects that do not have a __format__ method that handles it. See bpo-7994 for background.difflib.SequenceMatcher.isbjunk()
anddifflib.SequenceMatcher.isbpopular()
were deprecated in 3.2, and have now been removed: usex in sm.bjunk
andx in sm.bpopular
, where sm is aSequenceMatcher
object (bpo-13248).
Code Cleanups¶
The unused and undocumented internal
Scanner
class has been removed from thepydoc
module.The private and effectively unused
_gestalt
module has been removed, along with the privateplatform
functions_mac_ver_lookup
,_mac_ver_gstalt
, and_bcd2str
, which would only have ever been called on badly broken OSX systems (see bpo-18393).The hardcoded copies of certain
stat
constants that were included in thetarfile
module namespace have been removed.
Porting to Python 3.4¶
This section lists previously described changes and other bugfixes that may require changes to your code.
Changes in ‘python’ Command Behavior¶
In a posix shell, setting the
PATH
environment variable to an empty value is equivalent to not setting it at all. However, settingPYTHONPATH
to an empty value was not equivalent to not setting it at all: settingPYTHONPATH
to an empty value was equivalent to setting it to.
, which leads to confusion when reasoning by analogy to howPATH
works. The behavior now conforms to the posix convention forPATH
.The [X refs, Y blocks] output of a debug (
--with-pydebug
) build of the CPython interpreter is now off by default. It can be re-enabled using the-X showrefcount
option. (Contributed by Ezio Melotti in bpo-17323.)The python command and most stdlib scripts (as well as
argparse
) now output--version
information tostdout
instead ofstderr
(for issue list see Other Improvements above).
Changes in the Python API¶
The ABCs defined in
importlib.abc
now either raise the appropriate exception or return a default value instead of raisingNotImplementedError
blindly. This will only affect code callingsuper()
and falling through all the way to the ABCs. For compatibility, catch bothNotImplementedError
or the appropriate exception as needed.The module type now initializes the
__package__
and__loader__
attributes toNone
by default. To determine if these attributes were set in a backwards-compatible fashion, use e.g.getattr(module, '__loader__', None) is not None
. (bpo-17115.)importlib.util.module_for_loader()
now sets__loader__
and__package__
unconditionally to properly support reloading. If this is not desired then you will need to set these attributes manually. You can useimportlib.util.module_to_load()
for module management.Import now resets relevant attributes (e.g.
__name__
,__loader__
,__package__
,__file__
,__cached__
) unconditionally when reloading. Note that this restores a pre-3.3 behavior in that it means a module is re-found when re-loaded (bpo-19413).Frozen packages no longer set
__path__
to a list containing the package name, they now set it to an empty list. The previous behavior could cause the import system to do the wrong thing on submodule imports if there was also a directory with the same name as the frozen package. The correct way to determine if a module is a package or not is to usehasattr(module, '__path__')
(bpo-18065).Frozen modules no longer define a
__file__
attribute. It’s semantically incorrect for frozen modules to set the attribute as they are not loaded from any explicit location. If you must know that a module comes from frozen code then you can see if the module’s__spec__.location
is set to'frozen'
, check if the loader is a subclass ofimportlib.machinery.FrozenImporter
, or if Python 2 compatibility is necessary you can useimp.is_frozen()
.py_compile.compile()
now raisesFileExistsError
if the file path it would write to is a symlink or a non-regular file. This is to act as a warning that import will overwrite those files with a regular file regardless of what type of file path they were originally.importlib.abc.SourceLoader.get_source()
no longer raisesImportError
when the source code being loaded triggers aSyntaxError
orUnicodeDecodeError
. AsImportError
is meant to be raised only when source code cannot be found but it should, it was felt to be over-reaching/overloading of that meaning when the source code is found but improperly structured. If you were catching ImportError before and wish to continue to ignore syntax or decoding issues, catch all three exceptions now.functools.update_wrapper()
andfunctools.wraps()
now correctly set the__wrapped__
attribute to the function being wrapped, even if that function also had its__wrapped__
attribute set. This means__wrapped__
attributes now correctly link a stack of decorated functions rather than every__wrapped__
attribute in the chain referring to the innermost function. Introspection libraries that assumed the previous behaviour was intentional can useinspect.unwrap()
to access the first function in the chain that has no__wrapped__
attribute.inspect.getfullargspec()
has been reimplemented on top ofinspect.signature()
and hence handles a much wider variety of callable objects than it did in the past. It is expected that additional builtin and extension module callables will gain signature metadata over the course of the Python 3.4 series. Code that assumes thatinspect.getfullargspec()
will fail on non-Python callables may need to be adjusted accordingly.importlib.machinery.PathFinder
now passes on the current working directory to objects insys.path_hooks
for the empty string. This results insys.path_importer_cache
never containing''
, thus iterating throughsys.path_importer_cache
based onsys.path
will not find all keys. A module’s__file__
when imported in the current working directory will also now have an absolute path, including when using-m
with the interpreter (except for__main__.__file__
when a script has been executed directly using a relative path) (Contributed by Brett Cannon in bpo-18416). is specified on the command-line) (bpo-18416).The removal of the strict argument to
HTTPConnection
andHTTPSConnection
changes the meaning of the remaining arguments if you are specifying them positionally rather than by keyword. If you’ve been paying attention to deprecation warnings your code should already be specifying any additional arguments via keywords.Strings between
from __future__ import ...
statements now always raise aSyntaxError
. Previously if there was no leading docstring, an interstitial string would sometimes be ignored. This brings CPython into compliance with the language spec; Jython and PyPy already were. (bpo-17434).ssl.SSLSocket.getpeercert()
andssl.SSLSocket.do_handshake()
now raise anOSError
withENOTCONN
when theSSLSocket
is not connected, instead of the previous behavior of raising anAttributeError
. In addition,getpeercert()
will raise aValueError
if the handshake has not yet been done.base64.b32decode()
now raises abinascii.Error
when the input string contains non-b32-alphabet characters, instead of aTypeError
. This particularTypeError
was missed when the otherTypeError
s were converted. (Contributed by Serhiy Storchaka in bpo-18011.) Note: this change was also inadvertently applied in Python 3.3.3.The
file
attribute is now automatically closed when the creatingcgi.FieldStorage
instance is garbage collected. If you were pulling the file object out separately from thecgi.FieldStorage
instance and not keeping the instance alive, then you should either store the entirecgi.FieldStorage
instance or read the contents of the file before thecgi.FieldStorage
instance is garbage collected.Calling
read
orwrite
on a closed SSL socket now raises an informativeValueError
rather than the previous more mysteriousAttributeError
(bpo-9177).slice.indices()
no longer produces anOverflowError
for huge values. As a consequence of this fix,slice.indices()
now raises aValueError
if given a negative length; previously it returned nonsense values (bpo-14794).The
complex
constructor, unlike thecmath
functions, was incorrectly acceptingfloat
values if an object’s__complex__
special method returned one. This now raises aTypeError
. (bpo-16290.)The
int
constructor in 3.2 and 3.3 erroneously acceptsfloat
values for the base parameter. It is unlikely anyone was doing this, but if so, it will now raise aTypeError
(bpo-16772).Defaults for keyword-only arguments are now evaluated after defaults for regular keyword arguments, instead of before. Hopefully no one wrote any code that depends on the previous buggy behavior (bpo-16967).
Stale thread states are now cleared after
fork()
. This may cause some system resources to be released that previously were incorrectly kept perpetually alive (for example, database connections kept in thread-local storage). (bpo-17094.)Parameter names in
__annotations__
dicts are now mangled properly, similarly to__kwdefaults__
. (Contributed by Yury Selivanov in bpo-20625.)hashlib.hash.name
now always returns the identifier in lower case. Previously some builtin hashes had uppercase names, but now that it is a formal public interface the naming has been made consistent (bpo-18532).Because
unittest.TestSuite
now drops references to tests after they are run, test harnesses that reuse aTestSuite
to re-run a set of tests may fail. Test suites should not be re-used in this fashion since it means state is retained between test runs, breaking the test isolation thatunittest
is designed to provide. However, if the lack of isolation is considered acceptable, the old behavior can be restored by creating aTestSuite
subclass that defines a_removeTestAtIndex
method that does nothing (seeTestSuite.__iter__()
) (bpo-11798).unittest
now usesargparse
for command line parsing. There are certain invalid command forms that used to work that are no longer allowed; in theory this should not cause backward compatibility issues since the disallowed command forms didn’t make any sense and are unlikely to be in use.The
re.split()
,re.findall()
, andre.sub()
functions, and thegroup()
andgroups()
methods ofmatch
objects now always return a bytes object when the string to be matched is a bytes-like object. Previously the return type matched the input type, so if your code was depending on the return value being, say, abytearray
, you will need to change your code.audioop
functions now raise an error immediately if passed string input, instead of failing randomly later on (bpo-16685).The new convert_charrefs argument to
HTMLParser
currently defaults toFalse
for backward compatibility, but will eventually be changed to default toTrue
. It is recommended that you add this keyword, with the appropriate value, to anyHTMLParser
calls in your code (bpo-13633).Since the digestmod argument to the
hmac.new()
function will in the future have no default, all calls tohmac.new()
should be changed to explicitly specify a digestmod (bpo-17276).Calling
sysconfig.get_config_var()
with theSO
key, or lookingSO
up in the results of a call tosysconfig.get_config_vars()
is deprecated. This key should be replaced byEXT_SUFFIX
orSHLIB_SUFFIX
, depending on the context (bpo-19555).Any calls to
open
functions that specifyU
should be modified.U
is ineffective in Python3 and will eventually raise an error if used. Depending on the function, the equivalent of its old Python2 behavior can be achieved using either a newline argument, or if necessary by wrapping the stream inTextIOWrapper
to use its newline argument (bpo-15204).If you use
pyvenv
in a script and desire that pip not be installed, you must add--without-pip
to your command invocation.The default behavior of
json.dump()
andjson.dumps()
when an indent is specified has changed: it no longer produces trailing spaces after the item separating commas at the ends of lines. This will matter only if you have tests that are doing white-space-sensitive comparisons of such output (bpo-16333).doctest
now looks for doctests in extension module__doc__
strings, so if your doctest test discovery includes extension modules that have things that look like doctests in them you may see test failures you’ve never seen before when running your tests (bpo-3158).The
collections.abc
module has been slightly refactored as part of the Python startup improvements. As a consequence of this, it is no longer the case that importingcollections
automatically importscollections.abc
. If your program depended on the (undocumented) implicit import, you will need to add an explicitimport collections.abc
(bpo-20784).
Changes in the C API¶
PyEval_EvalFrameEx()
,PyObject_Repr()
, andPyObject_Str()
, along with some other internal C APIs, now include a debugging assertion that ensures they are not used in situations where they may silently discard a currently active exception. In cases where discarding the active exception is expected and desired (for example, because it has already been saved locally withPyErr_Fetch()
or is being deliberately replaced with a different exception), an explicitPyErr_Clear()
call will be needed to avoid triggering the assertion when invoking these operations (directly or indirectly) and running against a version of Python that is compiled with assertions enabled.PyErr_SetImportError()
now setsTypeError
when its msg argument is not set. Previously onlyNULL
was returned with no exception set.The result of the
PyOS_ReadlineFunctionPointer
callback must now be a string allocated byPyMem_RawMalloc()
orPyMem_RawRealloc()
, orNULL
if an error occurred, instead of a string allocated byPyMem_Malloc()
orPyMem_Realloc()
(bpo-16742)PyThread_set_key_value()
now always set the value. In Python 3.3, the function did nothing if the key already exists (if the current value is a non-NULL
pointer).The
f_tstate
(thread state) field of thePyFrameObject
structure has been removed to fix a bug: see bpo-14432 for the rationale.
Changed in 3.4.3¶
PEP 476: Enabling certificate verification by default for stdlib http clients¶
http.client
and modules which use it, such as urllib.request
and
xmlrpc.client
, will now verify that the server presents a certificate
which is signed by a CA in the platform trust store and whose hostname matches
the hostname being requested by default, significantly improving security for
many applications.
For applications which require the old previous behavior, they can pass an alternate context:
import urllib.request
import ssl
# This disables all verification
context = ssl._create_unverified_context()
# This allows using a specific certificate for the host, which doesn't need
# to be in the trust store
context = ssl.create_default_context(cafile="/path/to/file.crt")
urllib.request.urlopen("https://invalid-cert", context=context)

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