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pythonclassmethodsnamespaces
Troels Folke
Troels Folke

Reputation: 927

Method namespaces/collections in Python classes

Say I have a class Foo and I do foo = Foo(). I want some kind of "method namespace" foo.bar that is not shared across Foo instances, to which I dynamically can add methods that operate on foo:

def method(self, someValue):
    self.value = someValue + 10

foo.bar.m = method
foo.bar.m(20)

And then I want to find that foo.value is 30.

Any way to accomplish this?

Upvotes: 2

Views: 380

Answers (1)

Michael0x2a
Michael0x2a

Reputation: 64068

Is this what you're looking for?

import types

class Namespace(object):
    pass

class Foo(object):
    def __init__(self, value):
        self.value = value
        self.bar = Namespace()

def function(self, new_value):
    self.value = new_value

a = Foo(1)
b = Foo(2)

b.bar.function = types.MethodType(function, b, Foo)
b.bar.function(6)

print a.value   # prints 1
print b.value   # prints 6

The trick is using the types module to convert the test function into a method that can be bound to an instance of the object.

When I run this line: b.bar.function = types.MethodType(function, b, Foo), I am essentially telling Python to create a new method that binds function to the b instance of Foo. I can then take this method and store it inside any arbitrary location.

Since the method is permanently bound to the b instance of Foo, self will always refer to b regardless of which object the method is actually assigned to.

Upvotes: 3

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