Calling a method from a parent class in Python

Question

Can anyone help me with the correct syntax to call my method __get_except_lines(...) from the parent class?

I have a class with a method as shown below. This particular method has the 2 underscores because I don't want the "user" to use it.

NewPdb(object)
    myvar = ...
    ...
    def __init__(self):
        ...
    def __get_except_lines(self,...):
        ...

In a separate file I have another class that inherits from this class.

from new_pdb import NewPdb

    PdbLig(NewPdb):
        def __init__(self):
            ....
            self.cont = NewPdb.myvar
            self.cont2 = NewPdb.__get_except_lines(...)

And I get an attribute error that really confuses me:

AttributeError: type object 'NewPdb' has no attribute '_PdbLig__get_except_lines'

The problem is solved now thanks to @hivert. I really appreciate everyone's help here, again, I learned something new (name mangling)! Great community! — , Jul 17 '13 at 20:28

score 1 · Accepted Answer · answered Jul 17 '13 at 20:04

1

Your problem is due to Python name mangling for private variable (http://docs.python.org/2/tutorial/classes.html#private-variables-and-class-local-references). You should write:

NewPdb._NewPdb__get_except_lines(...)

answered Jul 17 '13 at 20:04

hivert

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score 0 · Answer 2 · answered Jul 17 '13 at 19:57

0

super(<your_class_name>, self).<method_name>(args)

e.g.

super(PdbLig, self).__get_except_lines(...)

answered Jul 17 '13 at 19:57

Maciej Gol

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Thanks, but now I get an `AttributeError: 'super' object has no attribute '_PdbLig__get_except_lines'`. I used `self.cont = super(NewPdb,self).__get_except_lines(...` – Jul 17 '13 at 20:20
It's because double underscores cause [name mangling](http://docs.python.org/release/1.5/tut/node67.html). If you want to keep your variable accessible, yet giving it internal meaning, add a single underscore - this is generaly known as `internally-used` indicator. – Maciej Gol Jul 17 '13 at 20:27

Marcin · Answer 3 · 2013-07-17T20:49:26.193

0

The entire point of putting a double underscore in front of a name is to prevent it from being called in a child class. See http://docs.python.org/2/tutorial/classes.html#private-variables-and-class-local-references

If you want to do this, then don't name it with a double underscore (you can use a single underscore), or create an alias for the name on the base class (thus again defeating the purpose).

edited Jul 17 '13 at 20:49

answered Jul 17 '13 at 20:15

Marcin

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Ah, okay makes sense now. The intention was that I have a parent class with this method, which (the method) should only used by myself in other methods. So I guess what I can do is just to copy&paste this method over into the child class, although it's not the "cleanest" way – Jul 17 '13 at 20:22
@SebastianRaschka Or just not use two underscores. – Marcin Jul 17 '13 at 20:24
I wanted to have those 2 underscores there for the "user" to know that this is one of the methods that he is not intended to use. – Jul 17 '13 at 20:42
1

@SebastianRaschka The convention in such a case is to use a single underscore. – Marcin Jul 17 '13 at 20:49
Thanks, I really didn't know that. Found a good thread here about singe and double underscore usage: http://stackoverflow.com/questions/6930144/underscore-vs-double-underscore-with-variables-and-methods – Jul 17 '13 at 21:32

Calling a method from a parent class in Python

3 Answers3