unable to read _version.py

Raise code

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 OSError:
        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
        )