def _do_eval(self, cmd, args):
        """\
        Evaluate python code.
            e <expr>        Evaluate <expr>.
        """
        code = args[0].lstrip()
        if not code:
            self.stderr.write('e: cannot evalutate empty expression\n')
            return
        try:
            eval(code)
        except:
            self.stderr.write('''When executing code '{}', the following error was raised:\n\n'''.format(code))
            self.stderr.write(textwrap.indent(traceback.format_exc(), '    '))
\
        Evaluate python code.
            e <expr>        Evaluate <expr>.