Validate url.

    :rtype: str
    :return: url

    :param str url: package homepage url.

def valid_url(url):
    """Validate url.

    :rtype: str
    :return: url

    :param str url: package homepage url.
    """
    regex = re.compile(
        r'^(?:http)s?://'
        r'(?:(?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+'
        r'(?:[A-Z]{2,6}\.?|[A-Z0-9-]{2,}\.?))'
        r'(?:/?|[/?]\S+)$', re.IGNORECASE)
    if not regex.match(url):
        raise argparse.ArgumentTypeError('"{0}" is invalid url.'.format(url))
    return url