def on_write(self, fd, callback):
        self.handlers[fd]['write'].append(callback)
        self._update_events(fd)
Validate if the string is not empty.
dataset/ETHPy150Open Shizmob/pydle/pydle/async.py/EventLoop.on_write--crossover with--dataset/ETHPy150Open mitsuhiko/fungiform/fungiform/forms.py/TextField.should_validate