Convert a file: URL to a path.

def url_to_path(url):
    # type: (str) -> str
    """
    Convert a file: URL to a path.
    """
    assert url.startswith('file:'), (
        "You can only turn file: urls into filenames (not %r)" % url)

    _, netloc, path, _, _ = urllib_parse.urlsplit(url)

    # if we have a UNC path, prepend UNC share notation
    if netloc:
        netloc = '\\\\' + netloc

    path = urllib_request.url2pathname(netloc + path)
    return path