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//lib/python2.7/site-packages/pip/_vendor/packaging/utils.py

# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
from __future__ import absolute_import, division, print_function

import re

from ._typing import MYPY_CHECK_RUNNING
from .version import InvalidVersion, Version

if MYPY_CHECK_RUNNING:  # pragma: no cover
    from typing import Union

_canonicalize_regex = re.compile(r"[-_.]+")

def canonicalize_name(name):
    # type: (str) -> str
    # This is taken from PEP 503.
    return _canonicalize_regex.sub("-", name).lower()

def canonicalize_version(_version):
    # type: (str) -> Union[Version, str]
    """
    This is very similar to Version.__str__, but has one subtle difference
    with the way it handles the release segment.
    """

try:
        version = Version(_version)
    except InvalidVersion:
        # Legacy versions cannot be normalized
        return _version

parts = []

# Epoch
    if version.epoch != 0:
        parts.append("{0}!".format(version.epoch))

# Release segment
    # NB: This strips trailing '.0's to normalize
    parts.append(re.sub(r"(\.0)+$", "", ".".join(str(x) for x in version.release)))

# Pre-release
    if version.pre is not None:
        parts.append("".join(str(x) for x in version.pre))

# Post-release
    if version.post is not None:
        parts.append(".post{0}".format(version.post))

# Development release
    if version.dev is not None:
        parts.append(".dev{0}".format(version.dev))

# Local version segment
    if version.local is not None:
        parts.append("+{0}".format(version.local))

return "".join(parts)