Question

Dictionaries and lists defined directly under the class definition act as static (e.g. this question)
How come other variables such as integer do not?

>>> class Foo():
        bar=1

>>> a=Foo()
>>> b=Foo()
>>> a.bar=4
>>> b.bar
1
>>> class Foo():
        bar={}

>>> a=Foo()
>>> b=Foo()
>>> a.bar[7]=8
>>> b.bar
{7: 8}

Answer 1

They are all class variables. Except for when you assigned a.bar=4 creating an instance variable. Basically Python has a lookup order on attributes. It goes:

instance -> class -> parent classes in MRO order (left to right)

So if you have

class Foo(object):
    bar = 1

This is a variable on the class Foo. Once you do

a = Foo()
a.bar = 2

you have created a new variable on the object a with the name bar. If you look at a.__class__.bar you will still see 1, but it is effectively hidden due to the order mentioned earlier.

The dict you created is at the class-level so it is shared between all instances of that class.