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What is the name of the method to override the [] operator (subscript notation) for a class in Python?

sophros
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Sahas
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3 Answers3

436

You need to use the __getitem__ method.

class MyClass:
    def __getitem__(self, key):
        return key * 2

myobj = MyClass()
myobj[3] #Output: 6

And if you're going to be setting values you'll need to implement the __setitem__ method too, otherwise this will happen:

>>> myobj[5] = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: MyClass instance has no attribute '__setitem__'
nairboon
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David Webb
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86

To fully overload it you also need to implement the __setitem__and __delitem__ methods.

edit

I almost forgot... if you want to completely emulate a list, you also need __getslice__, __setslice__ and __delslice__.

There are all documented in http://docs.python.org/reference/datamodel.html

Dave Kirby
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    `__getslice__, `__setslice__` and `__delslice__' have been deprecated for the last few releases of ver 2.x (not sure exactly when), and are no longer supported in ver 3.x. Instead, use `__getitem__`. `__setitem__` and `__delitem__' and test if the argument is of type `slice`, i.e.: `if isinstance(arg, slice): ... – Don O'Donnell Dec 25 '09 at 18:15
23

You are looking for the __getitem__ method. See http://docs.python.org/reference/datamodel.html, section 3.4.6

Confusion
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