Python Cmd module, subclassing issue

Question

I'm trying to work out what's not working in this code:

#!/usr/bin/python

import cmd

class My_class (cmd.Cmd):
    """docstring for Twitter_handler"""
    def __init__(self):
        super(My_class, self).__init__()

if __name__ == '__main__':
    my_handler = My_class()

Here's the error I get

Traceback (most recent call last):
  File "main.py", line 12, in <module>
    my_handler = My_class()
  File "main.py", line 9, in __init__
    super(My_class, self).__init__()
TypeError: super() argument 1 must be type, not classobj

If I change the superclass of "My_class" to an object it works fine. Where am I going wrong?

score 9 · Accepted Answer · answered Apr 20 '09 at 21:30

9

super() only works for new-style classes

answered Apr 20 '09 at 21:30

Patrick McElhaney

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score 8 · Answer 2 · edited Jun 16 '15 at 16:31

8

cmd.Cmd is not a new style class in Python 2.5, 2.6, 2.7.

Note that your code does not raise an exception in Python 3.0.

edited Jun 16 '15 at 16:31

Dave

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answered Apr 20 '09 at 21:32

Stephan202

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Is that because the cmd module is rewritten in Python 3? – Teifion Apr 20 '09 at 21:35
Nope. It's because in Python 3.0 all classes are "new style classes". – Stephan202 Apr 20 '09 at 21:39
(In fact, a diff between 2.5's and 3.0's cmd.py will show you that very few changes were made between those versions.) – Stephan202 Apr 20 '09 at 21:43
I wonder, could you change 'class Cmd:' in cmd.py to 'class Cmd(object)' and expect no problems? – John Fouhy Apr 21 '09 at 02:24
2

It would probably work. But you'd have the only python 2.x installation on earth with a new-style Cmd class... Don't let any code you ship depend on that :) – Stephan202 Apr 21 '09 at 06:15

score 2 · Answer 3 · edited Dec 11 '15 at 18:08

2

So if super() doesn't work use :

import cmd

class My_class(cmd.Cmd):
    def __init__(self):
        cmd.Cmd.__init__(self)

edited Dec 11 '15 at 18:08

Jonathon Reinhart

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answered Dec 01 '15 at 16:57

themadmax

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score 2 · Answer 4 · answered May 02 '16 at 15:08

2

You can still use super() if your MyClass extends object. This works even though the cmd.Cmd module is not a new-style class. Like this:

#!/usr/bin/python

import cmd

class My_class (cmd.Cmd, object):
    """docstring for Twitter_handler"""
    def __init__(self):
        super(My_class, self).__init__()

if __name__ == '__main__':
    my_handler = My_class()

answered May 02 '16 at 15:08

deargle

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This works for me as well. Can anyone weigh in on any weird side-effects in Py2 or Py3? – Technoloft Jul 26 '16 at 03:52

Python Cmd module, subclassing issue

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