def list_inputs(self):
        """Return a string listing all the Step's input names and their types.

        The types are returned in a copy/pastable format, so if the type is
        `string`, `'string'` (with single quotes) is returned.

        Returns:
            str containing all input names and types.
        """
        doc = []
        for inp, typ in self.input_types.items():
            if isinstance(typ, six.string_types):
                typ = "'{}'".format(typ)
            doc.append('{}: {}'.format(inp, typ))
        return '\n'.join(doc)
Return a string listing all the Step's input names and their types.

        The types are returned in a copy/pastable format, so if the type is
        `string`, `'string'` (with single quotes) is returned.

        Returns:
            str containing all input names and types.