>>> s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
>>> s.bind(('', 0))
>>> s.sendto(u'hellé', s.getsockname())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: sendto() takes exactly 3 arguments (2 given)
>>> s.sendto(3, s.getsockname())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: sendto() takes exactly 3 arguments (2 given)
>>> s.sendto('hello', s.getsockname())
5

The TypeError gives the wrong explanation for what's wrong.