Python class instance __dict__ doesn't contain all instance variables. Why?

Question

Here\'s a bit of a newbie Python question about instance variables.

Consider the following Python 2.7 class definition:

class Foo(object):
    a = 1
         


        

Answer 1

a is not an instance attribute, it's a class attribute.

Answer 2

May this help you further?

>>> class X(object):

    def __getattribute__(self, name):
        print name
        return object.__getattribute__(self, name)


>>> l = dir(X())
__dict__
__members__
__methods__
__class__
>>> l
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__']

Answer 3

Your a isn't an instance variable. You defined it as part of the class.

>>> class Foo(object):
...    a = 1
...
>>> Foo.a
1

If you want an instance variable you should put it inside the __init__ method, because this method is called when your object is created.