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# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import six
from oslo_config import cfg

__all__ = [
    'get_full_key_name',
    'check_key'
]


def get_full_key_name(key):
    """
    Return full metric key name, taking into account optional  prefix which can be specified in the
    config.
    """
    parts = ['st2']

    if cfg.CONF.metrics.prefix:
        parts.append(cfg.CONF.metrics.prefix)

    parts.append(key)

    return '.'.join(parts)


def check_key(key):
    """
    Ensure key meets requirements.
    """
    assert isinstance(key, six.string_types), "Key not a string. Got %s" % type(key)
    assert key, "Key cannot be empty string."

Add missing module.