I made a common mistake and ended up trying to subclass
a module. Here are two small python files:

----
a.py:

class a(object):
    pass

----
b.py:

import a

class B(a):  # Should be "a.a".
    pass
----
If I run "python b.py" I get the uninformative error
message:

Traceback (most recent call last):
  File "./b.py", line 3, in ?
    class B(a):
TypeError: function takes at most 2 arguments (3 given)

I think the message should say that "a" is not a class.