What are the differences amongst Python's “__g

Question

I just started learning Python a few months ago, and I'm trying to understand the differences between the different __get*__ methods:

__get__
__getattr__
__getattribute__
__getitem___

And their __del*__ equivalents:

__del__
__delattr__
__delete__
__delitem__

What are the differences between these? When should I use one over the other? Is there a specific reason why most of the __get*__ methods have __set*__ equivalents, but there is no __setattribute__?

Answer 1

The documentation for every method that you listed is easly reachable from the documentation index .

Anyway this may be a little extended reference:

__get__, __set__ and __del__ are descriptors

"In a nutshell, a descriptor is a way to customize what happens when you reference an attribute on a model." [official doc link]

They are well explained around, so here there are some references:

• Python Descriptors by Marty Alchin Part 1 and Part 2
• SO question Understanding __get__ and __set__ and Python descriptors
• google

__getattr__, __getattribute__, __setattr__, __delattr__

Are methods that can be defined to customize the meaning of attribute access (use of, assignment to, or deletion of x.name) for class instances. [official doc link]

Example 1:

class Foo:
    def __init__(self):
        self.x = 10
    def __getattr__(self, name):
        return name

f = Foo()
f.x    # -> 10
f.bar   # -> 'bar'

Example 2:

class Foo:
    def __init__(self):
        self.x = 10
    def __getattr__(self,name):
        return name
    def __getattribute__(self, name):
        if name == 'bar':
            raise AttributeError
        return 'getattribute'

f = Foo()
f.x    # -> 'getattribute'
f.baz    # -> 'getattribute'
f.bar    # -> 'bar'

__getitem__, __setitem__, __delitem__

Are methods that can be defined to implement container objects. [official doc link]

Example:

class MyColors:
    def __init__(self):
        self._colors = {'yellow': 1, 'red': 2, 'blue': 3}
    def __getitem__(self, name):
        return self._colors.get(name, 100)

colors = MyColors()
colors['yellow']   # -> 1
colors['brown']    # -> 100

I hope this is enough to give you a general idea.