How to assign an operation like sum or substitute, etc., to a variable

I want to do something like

class A:
    def __init__( self, left, right, op ):
        self.left = left
        sel开发者_如何学Pythonf.right = right
        self.op = op
    def calculate( self ):
        self.number = op( self.left, self.right )
        return self.number

and use it, for example, like this:

a = A( 1, 2, + )
a2 = A( 2, 3, * )

I tried to do

op = +
op = __add__

but none of these worked. Can somebody tell is this possible (and if it is, how this is called, because I don't even know how to search it). Or the only possible way is to have a big, ugly if-else statement in calculate and check the value of op, which will be stored as str?

Thanks!

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See the operator module.

a = A( 1, 2, operator.add )

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Another way to do this would be to supply a lambda function as the third parameter:

a = A( 1, 2, lambda x,y: x + y)
b = A( 1, 2, lambda x,y: x * y)

This would allow you to support more complex operations, not present in the operator module.