@staticmethod
def get_useragent_string():
    """
        :return a string containing 'python-', the request library name, a slash and the library version.
        :example:
            - If version is available
            python-requests/2.0.0
            # If the version is not available:
            python-requests
        """
    raise NotImplementedError('get_useragent_string method must be implemented'
        )
