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I had a bug where I was relying on methods being equal to each other when using is. It turns out that's not the case:
>>> class What:
... def meth(self):
... pass
>>> What.meth is What.meth
True
>>> inst = What()
>>> inst.meth is inst.meth
False
Why is that the case? It works for regular functions:
>>> def func(): pass
>>> func is func
True
586
Methods that do not have an instance of the class as the first argument are known as unbound methods. As of Python 3.0, the unbound methods have been removed from the language. They are not bounded with any specific object of the class.
The __add__() method in Python specifies what happens when you call + on two objects. When you call obj1 + obj2, you are essentially calling obj1. __add__(obj2).
The __int__ method is called to implement the built-in int function. The __index__ method implements type conversion to an int when the object is used in a slice expression and the built-in hex , oct , and bin functions.
The __new__() is a static method of the object class. It has the following signature: object.__new__(class, *args, **kwargs) Code language: Python (python) The first argument of the __new__ method is the class of the new object that you want to create.
Method objects are created each time you access them. Functions act as descriptors, returning a method object when their .__get__ method is called:
>>> What.__dict__['meth']
<function What.meth at 0x10a6f9c80>
>>> What.__dict__['meth'].__get__(What(), What)
<bound method What.meth of <__main__.What object at 0x10a6f7b10>>
If you're on Python 3.8 or later, you can use == equality testing instead. On Python 3.8 and later, two methods are equal if their .__self__ and .__func__ attributes are identical objects (so if they wrap the same function, and are bound to the same instance, both tested with is).
Before 3.8, method == behaviour is inconsistent based on how the method was implemented - Python methods and one of the two C method types compare __self__ for equality instead of identity, while the other C method type compares __self__ by identity. See Python issue 1617161.
If you need to test that the methods represent the same underlying function, test their __func__ attributes:
>>> What.meth == What.meth # functions (or unbound methods in Python 2)
True
>>> What().meth == What.meth # bound method and function
False
>>> What().meth == What().meth # bound methods with *different* instances
False
>>> What().meth.__func__ == What().meth.__func__ # functions
True
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