super() fails with error: TypeError “argument 1 must be type, not classobj” when parent does not inherit from object

I get some error that I can’t figure out. Any clue what is wrong with my sample code?

class B:
    def meth(self, arg):
        print arg

class C(B):
    def meth(self, arg):
        super(C, self).meth(arg)

print C().meth(1)

I got the sample test code from help of ‘super’ built-in method.

Here is the error:

Traceback (most recent call last):
  File "./test.py", line 10, in ?
    print C().meth(1)
  File "./test.py", line 8, in meth
    super(C, self).meth(arg)
TypeError: super() argument 1 must be type, not classobj

FYI, here is the help(super) from python itself:

Help on class super in module __builtin__:

class super(object)
 |  super(type) -> unbound super object
 |  super(type, obj) -> bound super object; requires isinstance(obj, type)
 |  super(type, type2) -> bound super object; requires issubclass(type2, type)
 |  Typical use to call a cooperative superclass method:
 |  class C(B):
 |      def meth(self, arg):
 |          super(C, self).meth(arg)
 |

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

Your problem is that class B is not declared as a “new-style” class. Change it like so:

class B(object):

and it will work.

super() and all subclass/superclass stuff only works with new-style classes. I recommend you get in the habit of always typing that (object) on any class definition to make sure it is a new-style class.

Old-style classes (also known as “classic” classes) are always of type classobj; new-style classes are of type type. This is why you got the error message you saw:

TypeError: super() argument 1 must be type, not classobj

Try this to see for yourself:

class OldStyle:
    pass

class NewStyle(object):
    pass

print type(OldStyle)  # prints: <type 'classobj'>

print type(NewStyle) # prints <type 'type'>

Note that in Python 3.x, all classes are new-style. You can still use the syntax from the old-style classes but you get a new-style class. So, in Python 3.x you won’t have this problem.

Method 2

Also, if you can’t change class B, you can fix the error by using multiple inheritance.

class B:
    def meth(self, arg):
        print arg

class C(B, object):
    def meth(self, arg):
        super(C, self).meth(arg)

print C().meth(1)

Method 3

If the python version is 3.X, it’s okay.

I think your python version is 2.X, the super would work when adding this code

__metaclass__ = type

so the code is

__metaclass__ = type
class B:
    def meth(self, arg):
        print arg
class C(B):
    def meth(self, arg):
        super(C, self).meth(arg)
print C().meth(1)

Method 4

I was also faced by the posted issue when I used python 2.7. It is working very fine with python 3.4

To make it work in python 2.7 I have added the __metaclass__ = type attribute at the top of my program and it worked.

__metaclass__ : It eases the transition from old-style classes and new-style classes.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0