Python super() raises TypeError

user_31610 0
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In Python 2.5, the following code raises a TypeError:

>>> class X:
      def a(self):
        print "a"

>>> class Y(X):
      def a(self):
        super(Y,self).a()
        print "b"

>>> c = Y()
>>> c.a()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in a
TypeError: super() argument 1 must be type, not classobj

If I replace the class X with class X(object), it will work. What's the explanation for this?

super python-2.x inheritance python
4 Answers

The reason is that super() only operates on new-style classes, which in the 2.x series means extending from object:

>>> class X(object):
        def a(self):
            print 'a'

>>> class Y(X):
        def a(self):
            super(Y, self).a()
            print 'b'

>>> c = Y()
>>> c.a()
a
b
Cody_Brocious_49770

In addition, don't use super() unless you have to. It's not the general-purpose "right thing" to do with new-style classes that you might suspect.

There are times when you're expecting multiple inheritance and you might possibly want it, but until you know the hairy details of the MRO, best leave it alone and stick to:

 X.a(self)
user_189360

I tried the various X.a() methods; however, they seem to require an instance of X in order to perform a(), so I did X().a(self), which seems more complete than the previous answers, at least for the applications I've encountered. It doesn't seem to be a good way of handling the problem as there is unnecessary construction and destruction, but it works fine.

My specific application was Python's cmd.Cmd module, which is evidently not a NewStyle object for some reason.

Final Result:

X().a(self)
user_4833470
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