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Override Python's 'in' operator?

Posted by: admin November 1, 2017 Leave a comment

Questions:

If I am creating my own class in Python, what function should I define so as to allow the use of the ‘in’ operator, e.g.

class MyClass(object):
    ...

m = MyClass()

if 54 in m:
    ...
Answers:

MyClass.__contains__(self, item)

Questions:
Answers:

A more complete answer is:

class MyClass(object):

    def __init__(self):
        self.numbers = [1,2,3,4,54]

    def __contains__(self, key):
        return key in self.numbers

Here you would get True when asking if 54 was in m:

>>> m = MyClass()
>>> 54 in m
True  

See documentation on overloading __contains__.

Questions:
Answers:

You might also want to take a look at an infix operator override framework I was able to use to create a domain-specific language:

http://code.activestate.com/recipes/384122/