<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def contribute_to_class(self, cls, name):
 """ Makes sure thumbnail gets set when image field initialized. """

        super(SizedImageField, self).contribute_to_class(cls, name)
        signals.post_init.connect(self._set_thumbnail, sender=cls)