def versions_from_file(filename):
    """Try to determine the version from _version.py if present."""
    try:
        with open(filename) as f:
            contents = f.read()
    except EnvironmentError:
        raise NotThisMethod("unable to read _version.py")
    mo = re.search(r"version_json = '''\n(.*)'''  # END VERSION_JSON",
                   contents, re.M | re.S)
    if not mo:
        mo = re.search(r"version_json = '''\r\n(.*)'''  # END VERSION_JSON",
                       contents, re.M | re.S)
    if not mo:
        raise NotThisMethod("no version_json in _version.py")
    return json.loads(mo.group(1))
Try to determine the version from _version.py if present.
versioneer.py