Static variable vs Class variable

[Diez B. Roggisch]

> In point #3, you really bind a name to a value. As you probably know, in 
> Python, there are names and objects. The initial value of the name 'a' 
> is 1. It is an immutable object. The "+=" operator usually increments a 
> value of an object. However, because the 'int' type is immutable, the += 
> operator will rather rebind this variable to a newly created value. I 
> believe this is what is happening here.

Your believes aside, this is simply wrong. The statement

a += x

always leads to a rebinding of a to the result of the operation +. I 
presume you got confused by the somewhat arbitrary difference between

__add__

and


__iadd__

that somehow suggest there is an in-place-modification going on in case 
of mutables.

but as the following snippet shows - that's not the case:


class Foo(object):
     def __add__(self, o):
         return "__add__"

     def __iadd__(self, o):
         return "__iadd__"


a = Foo()
a += 1
print a

a = Foo()
b = Foo()
c = a + b
print c

So you see, the first += overrides a with the returned value of __iadd__.

The reason for the difference though is most probably what you yourself 
expected: thus it's possible to alter a mutable in place.

Diez