Python variable lookup

I am having troubles understand how variable lookup and assignment are done in Python. I have a few lines of code here to make my question concrete.

class Test:
    number = 0
    def __init__(self):
        self.number += 1
def main():
    number = 2
    def foo():
        # This line errors. In this scenario, foo has a local var "number". I am trying to assign "number"
        #  in foo's scope with another var named "number", beloning to foo's outer scope. According to 
        # Python's LEGB rule, shouldn't the var "number" on right hand sign of the "number = number + 1" 
        # statement be read from foo's outer scope then assigned to var "number" in foo's scope?
        # I konw I shouldn't have variables with the same name in inner and outer scopes. If the code in
        # foo didn't workHow come the code in Test__init__, which is similar to the code in foo, work?

        number = number + 1 
    test = Test()


it’s self.number, that makes a difference