Writes prompt message to output stream and
            reads line from standard input stream.

            `prompt_msg`
                Message to write.
            `newline`
                Append newline character to prompt message before writing.

            Return string.

def prompt(self, prompt_msg=None, newline=False):
        """ Writes prompt message to output stream and
            reads line from standard input stream.

            `prompt_msg`
                Message to write.
            `newline`
                Append newline character to prompt message before writing.

            Return string.
            """

        if prompt_msg is not None:
            self.write(prompt_msg, newline)

        return self._input.readline().rstrip(os.linesep)