: Representing an email message

email.message
: Representing an email message¶
Source code: Lib/email/message.py
Added in version 3.6: [1]
The central class in the email
package is the EmailMessage
class, imported from the email.message
module. It is the base class for
the email
object model. EmailMessage
provides the core
functionality for setting and querying header fields, for accessing message
bodies, and for creating or modifying structured messages.
An email message consists of headers and a payload (which is also referred to as the content). Headers are RFC 5322 or RFC 6532 style field names and values, where the field name and value are separated by a colon. The colon is not part of either the field name or the field value. The payload may be a simple text message, or a binary object, or a structured sequence of sub-messages each with their own set of headers and their own payload. The latter type of payload is indicated by the message having a MIME type such as multipart/* or message/rfc822.
The conceptual model provided by an EmailMessage
object is that of an
ordered dictionary of headers coupled with a payload that represents the
RFC 5322 body of the message, which might be a list of sub-EmailMessage
objects. In addition to the normal dictionary methods for accessing the header
names and values, there are methods for accessing specialized information from
the headers (for example the MIME content type), for operating on the payload,
for generating a serialized version of the message, and for recursively walking
over the object tree.
The EmailMessage
dictionary-like interface is indexed by the header
names, which must be ASCII values. The values of the dictionary are strings
with some extra methods. Headers are stored and returned in case-preserving
form, but field names are matched case-insensitively. The keys are ordered,
but unlike a real dict, there can be duplicates. Additional methods are
provided for working with headers that have duplicate keys.
The payload is either a string or bytes object, in the case of simple message
objects, or a list of EmailMessage
objects, for MIME container
documents such as multipart/* and message/rfc822
message objects.
- class email.message.EmailMessage(policy=default)¶
If policy is specified use the rules it specifies to update and serialize the representation of the message. If policy is not set, use the
default
policy, which follows the rules of the email RFCs except for line endings (instead of the RFC mandated\r\n
, it uses the Python standard\n
line endings). For more information see thepolicy
documentation. [2]- as_string(unixfrom=False, maxheaderlen=None, policy=None)¶
Return the entire message flattened as a string. When optional unixfrom is true, the envelope header is included in the returned string. unixfrom defaults to
False
. For backward compatibility with the baseMessage
class maxheaderlen is accepted, but defaults toNone
, which means that by default the line length is controlled by themax_line_length
of the policy. The policy argument may be used to override the default policy obtained from the message instance. This can be used to control some of the formatting produced by the method, since the specified policy will be passed to theGenerator
.Flattening the message may trigger changes to the
EmailMessage
if defaults need to be filled in to complete the transformation to a string (for example, MIME boundaries may be generated or modified).Note that this method is provided as a convenience and may not be the most useful way to serialize messages in your application, especially if you are dealing with multiple messages. See
email.generator.Generator
for a more flexible API for serializing messages. Note also that this method is restricted to producing messages serialized as “7 bit clean” whenutf8
isFalse
, which is the default.Changed in version 3.6: the default behavior when maxheaderlen is not specified was changed from defaulting to 0 to defaulting to the value of max_line_length from the policy.
- __str__()¶
Equivalent to
as_string(policy=self.policy.clone(utf8=True))
. Allowsstr(msg)
to produce a string containing the serialized message in a readable format.Changed in version 3.4: the method was changed to use
utf8=True
, thus producing an RFC 6531-like message representation, instead of being a direct alias foras_string()
.
- as_bytes(unixfrom=False, policy=None)¶
Return the entire message flattened as a bytes object. When optional unixfrom is true, the envelope header is included in the returned string. unixfrom defaults to
False
. The policy argument may be used to override the default policy obtained from the message instance. This can be used to control some of the formatting produced by the method, since the specified policy will be passed to theBytesGenerator
.Flattening the message may trigger changes to the
EmailMessage
if defaults need to be filled in to complete the transformation to a string (for example, MIME boundaries may be generated or modified).Note that this method is provided as a convenience and may not be the most useful way to serialize messages in your application, especially if you are dealing with multiple messages. See
email.generator.BytesGenerator
for a more flexible API for serializing messages.
- __bytes__()¶
Equivalent to
as_bytes()
. Allowsbytes(msg)
to produce a bytes object containing the serialized message.
- is_multipart()¶
Return
True
if the message’s payload is a list of sub-EmailMessage
objects, otherwise returnFalse
. Whenis_multipart()
returnsFalse
, the payload should be a string object (which might be a CTE encoded binary payload). Note thatis_multipart()
returningTrue
does not necessarily mean that “msg.get_content_maintype() == ‘multipart’” will return theTrue
. For example,is_multipart
will returnTrue
when theEmailMessage
is of typemessage/rfc822
.
- set_unixfrom(unixfrom)¶
Set the message’s envelope header to unixfrom, which should be a string. (See
mboxMessage
for a brief description of this header.)
- get_unixfrom()¶
Return the message’s envelope header. Defaults to
None
if the envelope header was never set.
The following methods implement the mapping-like interface for accessing the message’s headers. Note that there are some semantic differences between these methods and a normal mapping (i.e. dictionary) interface. For example, in a dictionary there are no duplicate keys, but here there may be duplicate message headers. Also, in dictionaries there is no guaranteed order to the keys returned by
keys()
, but in anEmailMessage
object, headers are always returned in the order they appeared in the original message, or in which they were added to the message later. Any header deleted and then re-added is always appended to the end of the header list.These semantic differences are intentional and are biased toward convenience in the most common use cases.
Note that in all cases, any envelope header present in the message is not included in the mapping interface.
- __len__()¶
Return the total number of headers, including duplicates.
- __contains__(name)¶
Return
True
if the message object has a field named name. Matching is done without regard to case and name does not include the trailing colon. Used for thein
operator. For example:if 'message-id' in myMessage: print('Message-ID:', myMessage['message-id'])
- __getitem__(name)¶
Return the value of the named header field. name does not include the colon field separator. If the header is missing,
None
is returned; aKeyError
is never raised.Note that if the named field appears more than once in the message’s headers, exactly which of those field values will be returned is undefined. Use the
get_all()
method to get the values of all the extant headers named name.Using the standard (non-
compat32
) policies, the returned value is an instance of a subclass ofemail.headerregistry.BaseHeader
.
- __setitem__(name, val)¶
Add a header to the message with field name name and value val. The field is appended to the end of the message’s existing headers.
Note that this does not overwrite or delete any existing header with the same name. If you want to ensure that the new header is the only one present in the message with field name name, delete the field first, e.g.:
del msg['subject'] msg['subject'] = 'Python roolz!'
If the
policy
defines certain headers to be unique (as the standard policies do), this method may raise aValueError
when an attempt is made to assign a value to such a header when one already exists. This behavior is intentional for consistency’s sake, but do not depend on it as we may choose to make such assignments do an automatic deletion of the existing header in the future.
- __delitem__(name)¶
Delete all occurrences of the field with name name from the message’s headers. No exception is raised if the named field isn’t present in the headers.
- keys()¶
Return a list of all the message’s header field names.
- values()¶
Return a list of all the message’s field values.
- items()¶
Return a list of 2-tuples containing all the message’s field headers and values.
- get(name, failobj=None)¶
Return the value of the named header field. This is identical to
__getitem__()
except that optional failobj is returned if the named header is missing (failobj defaults toNone
).
Here are some additional useful header related methods:
- get_all(name, failobj=None)¶
Return a list of all the values for the field named name. If there are no such named headers in the message, failobj is returned (defaults to
None
).
- add_header(_name, _value, **_params)¶
Extended header setting. This method is similar to
__setitem__()
except that additional header parameters can be provided as keyword arguments. _name is the header field to add and _value is the primary value for the header.For each item in the keyword argument dictionary _params, the key is taken as the parameter name, with underscores converted to dashes (since dashes are illegal in Python identifiers). Normally, the parameter will be added as
key="value"
unless the value isNone
, in which case only the key will be added.If the value contains non-ASCII characters, the charset and language may be explicitly controlled by specifying the value as a three tuple in the format
(CHARSET, LANGUAGE, VALUE)
, whereCHARSET
is a string naming the charset to be used to encode the value,LANGUAGE
can usually be set toNone
or the empty string (see RFC 2231 for other possibilities), andVALUE
is the string value containing non-ASCII code points. If a three tuple is not passed and the value contains non-ASCII characters, it is automatically encoded in RFC 2231 format using aCHARSET
ofutf-8
and aLANGUAGE
ofNone
.Here is an example:
msg.add_header('Content-Disposition', 'attachment', filename='bud.gif')
This will add a header that looks like
Content-Disposition: attachment; filename="bud.gif"
An example of the extended interface with non-ASCII characters:
msg.add_header('Content-Disposition', 'attachment', filename=('iso-8859-1', '', 'Fußballer.ppt'))
- replace_header(_name, _value)¶
Replace a header. Replace the first header found in the message that matches _name, retaining header order and field name case of the original header. If no matching header is found, raise a
KeyError
.
- get_content_type()¶
Return the message’s content type, coerced to lower case of the form maintype/subtype. If there is no Content-Type header in the message return the value returned by
get_default_type()
. If the Content-Type header is invalid, returntext/plain
.(According to RFC 2045, messages always have a default type,
get_content_type()
will always return a value. RFC 2045 defines a message’s default type to be text/plain unless it appears inside a multipart/digest container, in which case it would be message/rfc822. If the Content-Type header has an invalid type specification, RFC 2045 mandates that the default type be text/plain.)
- get_content_maintype()¶
Return the message’s main content type. This is the maintype part of the string returned by
get_content_type()
.
- get_content_subtype()¶
Return the message’s sub-content type. This is the subtype part of the string returned by
get_content_type()
.
- get_default_type()¶
Return the default content type. Most messages have a default content type of text/plain, except for messages that are subparts of multipart/digest containers. Such subparts have a default content type of message/rfc822.
- set_default_type(ctype)¶
Set the default content type. ctype should either be text/plain or message/rfc822, although this is not enforced. The default content type is not stored in the Content-Type header, so it only affects the return value of the
get_content_type
methods when no Content-Type header is present in the message.
- set_param(param, value, header='Content-Type', requote=True, charset=None, language='', replace=False)¶
Set a parameter in the Content-Type header. If the parameter already exists in the header, replace its value with value. When header is
Content-Type
(the default) and the header does not yet exist in the message, add it, set its value to text/plain, and append the new parameter value. Optional header specifies an alternative header to Content-Type.If the value contains non-ASCII characters, the charset and language may be explicitly specified using the optional charset and language parameters. Optional language specifies the RFC 2231 language, defaulting to the empty string. Both charset and language should be strings. The default is to use the
utf8
charset andNone
for the language.If replace is
False
(the default) the header is moved to the end of the list of headers. If replace isTrue
, the header will be updated in place.Use of the requote parameter with
EmailMessage
objects is deprecated.Note that existing parameter values of headers may be accessed through the
params
attribute of the header value (for example,msg['Content-Type'].params['charset']
).Changed in version 3.4:
replace
keyword was added.
- del_param(param, header='content-type', requote=True)¶
Remove the given parameter completely from the Content-Type header. The header will be re-written in place without the parameter or its value. Optional header specifies an alternative to Content-Type.
Use of the requote parameter with
EmailMessage
objects is deprecated.
- get_filename(failobj=None)¶
Return the value of the
filename
parameter of the Content-Disposition header of the message. If the header does not have afilename
parameter, this method falls back to looking for thename
parameter on the Content-Type header. If neither is found, or the header is missing, then failobj is returned. The returned string will always be unquoted as peremail.utils.unquote()
.
- get_boundary(failobj=None)¶
Return the value of the
boundary
parameter of the Content-Type header of the message, or failobj if either the header is missing, or has noboundary
parameter. The returned string will always be unquoted as peremail.utils.unquote()
.
- set_boundary(boundary)¶
Set the
boundary
parameter of the Content-Type header to boundary.set_boundary()
will always quote boundary if necessary. AHeaderParseError
is raised if the message object has no Content-Type header.Note that using this method is subtly different from deleting the old Content-Type header and adding a new one with the new boundary via
add_header()
, becauseset_boundary()
preserves the order of the Content-Type header in the list of headers.
- get_content_charset(failobj=None)¶
Return the
charset
parameter of the Content-Type header, coerced to lower case. If there is no Content-Type header, or if that header has nocharset
parameter, failobj is returned.
- get_charsets(failobj=None)¶
Return a list containing the character set names in the message. If the message is a multipart, then the list will contain one element for each subpart in the payload, otherwise, it will be a list of length 1.
Each item in the list will be a string which is the value of the
charset
parameter in the Content-Type header for the represented subpart. If the subpart has no Content-Type header, nocharset
parameter, or is not of the text main MIME type, then that item in the returned list will be failobj.
- is_attachment()¶
Return
True
if there is a Content-Disposition header and its (case insensitive) value isattachment
,False
otherwise.Changed in version 3.4.2: is_attachment is now a method instead of a property, for consistency with
is_multipart()
.
- get_content_disposition()¶
Return the lowercased value (without parameters) of the message’s Content-Disposition header if it has one, or
None
. The possible values for this method are inline, attachment orNone
if the message follows RFC 2183.Added in version 3.5.
The following methods relate to interrogating and manipulating the content (payload) of the message.
- walk()¶
The
walk()
method is an all-purpose generator which can be used to iterate over all the parts and subparts of a message object tree, in depth-first traversal order. You will typically usewalk()
as the iterator in afor
loop; each iteration returns the next subpart.Here’s an example that prints the MIME type of every part of a multipart message structure:
>>> for part in msg.walk(): ... print(part.get_content_type()) multipart/report text/plain message/delivery-status text/plain text/plain message/rfc822 text/plain
walk
iterates over the subparts of any part whereis_multipart()
returnsTrue
, even thoughmsg.get_content_maintype() == 'multipart'
may returnFalse
. We can see this in our example by making use of the_structure
debug helper function:>>> from email.iterators import _structure >>> for part in msg.walk(): ... print(part.get_content_maintype() == 'multipart', ... part.is_multipart()) True True False False False True False False False False False True False False >>> _structure(msg) multipart/report text/plain message/delivery-status text/plain text/plain message/rfc822 text/plain
Here the
message
parts are notmultiparts
, but they do contain subparts.is_multipart()
returnsTrue
andwalk
descends into the subparts.
- get_body(preferencelist=('related', 'html', 'plain'))¶
Return the MIME part that is the best candidate to be the “body” of the message.
preferencelist must be a sequence of strings from the set
related
,html
, andplain
, and indicates the order of preference for the content type of the part returned.Start looking for candidate matches with the object on which the
get_body
method is called.If
related
is not included in preferencelist, consider the root part (or subpart of the root part) of any related encountered as a candidate if the (sub-)part matches a preference.When encountering a
multipart/related
, check thestart
parameter and if a part with a matching Content-ID is found, consider only it when looking for candidate matches. Otherwise consider only the first (default root) part of themultipart/related
.If a part has a Content-Disposition header, only consider the part a candidate match if the value of the header is
inline
.If none of the candidates matches any of the preferences in preferencelist, return
None
.Notes: (1) For most applications the only preferencelist combinations that really make sense are
('plain',)
,('html', 'plain')
, and the default('related', 'html', 'plain')
. (2) Because matching starts with the object on whichget_body
is called, callingget_body
on amultipart/related
will return the object itself unless preferencelist has a non-default value. (3) Messages (or message parts) that do not specify a Content-Type or whose Content-Type header is invalid will be treated as if they are of typetext/plain
, which may occasionally causeget_body
to return unexpected results.
- iter_attachments()¶
Return an iterator over all of the immediate sub-parts of the message that are not candidate “body” parts. That is, skip the first occurrence of each of
text/plain
,text/html
,multipart/related
, ormultipart/alternative
(unless they are explicitly marked as attachments via Content-Disposition: attachment), and return all remaining parts. When applied directly to amultipart/related
, return an iterator over the all the related parts except the root part (ie: the part pointed to by thestart
parameter, or the first part if there is nostart
parameter or thestart
parameter doesn’t match the Content-ID of any of the parts). When applied directly to amultipart/alternative
or a non-multipart
, return an empty iterator.
- iter_parts()¶
Return an iterator over all of the immediate sub-parts of the message, which will be empty for a non-
multipart
. (See alsowalk()
.)
- get_content(*args, content_manager=None, **kw)¶
Call the
get_content()
method of the content_manager, passing self as the message object, and passing along any other arguments or keywords as additional arguments. If content_manager is not specified, use thecontent_manager
specified by the currentpolicy
.
- set_content(*args, content_manager=None, **kw)¶
Call the
set_content()
method of the content_manager, passing self as the message object, and passing along any other arguments or keywords as additional arguments. If content_manager is not specified, use thecontent_manager
specified by the currentpolicy
.
Convert a non-
multipart
message into amultipart/related
message, moving any existing Content- headers and payload into a (new) first part of themultipart
. If boundary is specified, use it as the boundary string in the multipart, otherwise leave the boundary to be automatically created when it is needed (for example, when the message is serialized).
- make_alternative(boundary=None)¶
Convert a non-
multipart
or amultipart/related
into amultipart/alternative
, moving any existing Content- headers and payload into a (new) first part of themultipart
. If boundary is specified, use it as the boundary string in the multipart, otherwise leave the boundary to be automatically created when it is needed (for example, when the message is serialized).
- make_mixed(boundary=None)¶
Convert a non-
multipart
, amultipart/related
, or amultipart-alternative
into amultipart/mixed
, moving any existing Content- headers and payload into a (new) first part of themultipart
. If boundary is specified, use it as the boundary string in the multipart, otherwise leave the boundary to be automatically created when it is needed (for example, when the message is serialized).
If the message is a
multipart/related
, create a new message object, pass all of the arguments to itsset_content()
method, andattach()
it to themultipart
. If the message is a non-multipart
, callmake_related()
and then proceed as above. If the message is any other type ofmultipart
, raise aTypeError
. If content_manager is not specified, use thecontent_manager
specified by the currentpolicy
. If the added part has no Content-Disposition header, add one with the valueinline
.
- add_alternative(*args, content_manager=None, **kw)¶
If the message is a
multipart/alternative
, create a new message object, pass all of the arguments to itsset_content()
method, andattach()
it to themultipart
. If the message is a non-multipart
ormultipart/related
, callmake_alternative()
and then proceed as above. If the message is any other type ofmultipart
, raise aTypeError
. If content_manager is not specified, use thecontent_manager
specified by the currentpolicy
.
- add_attachment(*args, content_manager=None, **kw)¶
If the message is a
multipart/mixed
, create a new message object, pass all of the arguments to itsset_content()
method, andattach()
it to themultipart
. If the message is a non-multipart
,multipart/related
, ormultipart/alternative
, callmake_mixed()
and then proceed as above. If content_manager is not specified, use thecontent_manager
specified by the currentpolicy
. If the added part has no Content-Disposition header, add one with the valueattachment
. This method can be used both for explicit attachments (Content-Disposition: attachment) andinline
attachments (Content-Disposition: inline), by passing appropriate options to thecontent_manager
.
- clear()¶
Remove the payload and all of the headers.
- clear_content()¶
Remove the payload and all of the !Content- headers, leaving all other headers intact and in their original order.
EmailMessage
objects have the following instance attributes:- preamble¶
The format of a MIME document allows for some text between the blank line following the headers, and the first multipart boundary string. Normally, this text is never visible in a MIME-aware mail reader because it falls outside the standard MIME armor. However, when viewing the raw text of the message, or when viewing the message in a non-MIME aware reader, this text can become visible.
The preamble attribute contains this leading extra-armor text for MIME documents. When the
Parser
discovers some text after the headers but before the first boundary string, it assigns this text to the message’s preamble attribute. When theGenerator
is writing out the plain text representation of a MIME message, and it finds the message has a preamble attribute, it will write this text in the area between the headers and the first boundary. Seeemail.parser
andemail.generator
for details.Note that if the message object has no preamble, the preamble attribute will be
None
.
- epilogue¶
The epilogue attribute acts the same way as the preamble attribute, except that it contains text that appears between the last boundary and the end of the message. As with the
preamble
, if there is no epilog text this attribute will beNone
.
- defects¶
The defects attribute contains a list of all the problems found when parsing this message. See
email.errors
for a detailed description of the possible parsing defects.
- class email.message.MIMEPart(policy=default)¶
This class represents a subpart of a MIME message. It is identical to
EmailMessage
, except that no MIME-Version headers are added whenset_content()
is called, since sub-parts do not need their own MIME-Version headers.
Footnotes


Queues

Queues¶
Source code: Lib/asyncio/queues.py
asyncio queues are designed to be similar to classes of the
queue
module. Although asyncio queues are not thread-safe,
they are designed to be used specifically in async/await code.
Note that methods of asyncio queues don’t have a timeout parameter;
use asyncio.wait_for()
function to do queue operations with a
timeout.
See also the Examples section below.
Queue¶
- class asyncio.Queue(maxsize=0)¶
A first in, first out (FIFO) queue.
If maxsize is less than or equal to zero, the queue size is infinite. If it is an integer greater than
0
, thenawait put()
blocks when the queue reaches maxsize until an item is removed byget()
.Unlike the standard library threading
queue
, the size of the queue is always known and can be returned by calling theqsize()
method.Changed in version 3.10: Removed the loop parameter.
This class is not thread safe.
- maxsize¶
Number of items allowed in the queue.
- empty()¶
Return
True
if the queue is empty,False
otherwise.
- full()¶
Return
True
if there aremaxsize
items in the queue.If the queue was initialized with
maxsize=0
(the default), thenfull()
never returnsTrue
.
- async get()¶
Remove and return an item from the queue. If queue is empty, wait until an item is available.
Raises
QueueShutDown
if the queue has been shut down and is empty, or if the queue has been shut down immediately.
- get_nowait()¶
Return an item if one is immediately available, else raise
QueueEmpty
.
- async join()¶
Block until all items in the queue have been received and processed.
The count of unfinished tasks goes up whenever an item is added to the queue. The count goes down whenever a consumer coroutine calls
task_done()
to indicate that the item was retrieved and all work on it is complete. When the count of unfinished tasks drops to zero,join()
unblocks.
- async put(item)¶
Put an item into the queue. If the queue is full, wait until a free slot is available before adding the item.
Raises
QueueShutDown
if the queue has been shut down.
- put_nowait(item)¶
Put an item into the queue without blocking.
If no free slot is immediately available, raise
QueueFull
.
- qsize()¶
Return the number of items in the queue.
- shutdown(immediate=False)¶
Put a
Queue
instance into a shutdown mode.The queue can no longer grow. Future calls to
put()
raiseQueueShutDown
. Currently blocked callers ofput()
will be unblocked and will raiseQueueShutDown
in the formerly awaiting task.If immediate is false (the default), the queue can be wound down normally with
get()
calls to extract tasks that have already been loaded.And if
task_done()
is called for each remaining task, a pendingjoin()
will be unblocked normally.Once the queue is empty, future calls to
get()
will raiseQueueShutDown
.If immediate is true, the queue is terminated immediately. The queue is drained to be completely empty and the count of unfinished tasks is reduced by the number of tasks drained. If unfinished tasks is zero, callers of
join()
are unblocked. Also, blocked callers ofget()
are unblocked and will raiseQueueShutDown
because the queue is empty.Use caution when using
join()
with immediate set to true. This unblocks the join even when no work has been done on the tasks, violating the usual invariant for joining a queue.Added in version 3.13.
- task_done()¶
Indicate that a formerly enqueued work item is complete.
Used by queue consumers. For each
get()
used to fetch a work item, a subsequent call totask_done()
tells the queue that the processing on the work item is complete.If a
join()
is currently blocking, it will resume when all items have been processed (meaning that atask_done()
call was received for every item that had beenput()
into the queue).Raises
ValueError
if called more times than there were items placed in the queue.
Priority Queue¶
LIFO Queue¶
Exceptions¶
- exception asyncio.QueueEmpty¶
This exception is raised when the
get_nowait()
method is called on an empty queue.
- exception asyncio.QueueFull¶
Exception raised when the
put_nowait()
method is called on a queue that has reached its maxsize.
Examples¶
Queues can be used to distribute workload between several concurrent tasks:
import asyncio
import random
import time
async def worker(name, queue):
while True:
# Get a "work item" out of the queue.
sleep_for = await queue.get()
# Sleep for the "sleep_for" seconds.
await asyncio.sleep(sleep_for)
# Notify the queue that the "work item" has been processed.
queue.task_done()
print(f'{name} has slept for {sleep_for:.2f} seconds')
async def main():
# Create a queue that we will use to store our "workload".
queue = asyncio.Queue()
# Generate random timings and put them into the queue.
total_sleep_time = 0
for _ in range(20):
sleep_for = random.uniform(0.05, 1.0)
total_sleep_time += sleep_for
queue.put_nowait(sleep_for)
# Create three worker tasks to process the queue concurrently.
tasks = []
for i in range(3):
task = asyncio.create_task(worker(f'worker-{i}', queue))
tasks.append(task)
# Wait until the queue is fully processed.
started_at = time.monotonic()
await queue.join()
total_slept_for = time.monotonic() - started_at
# Cancel our worker tasks.
for task in tasks:
task.cancel()
# Wait until all worker tasks are cancelled.
await asyncio.gather(*tasks, return_exceptions=True)
print('====')
print(f'3 workers slept in parallel for {total_slept_for:.2f} seconds')
print(f'total expected sleep time: {total_sleep_time:.2f} seconds')
asyncio.run(main())