gistfile1.py

    def assert_file_like_object(self, obj):
        interface = set(('open', 'close', 'encoding', 'fileno', 'flush', 'isatty',
                         'newlines', 'read', 'readinto', 'readline', 'readlines',
                         'seek', 'softspace', 'tell', 'truncate', 'write', 'writelines',
                         'xreadlines', 'name'))
        methods = set(dir(obj))

        has_valid_api = interface.issubset(methods)
        missing_methods = ', '.join(interface.difference(methods))

        self.assertTrue(has_valid_api,
                        "{0} should be file-like object. Missing methods/attributes: {1}"
                        .format(obj, missing_methods))