Why is there a local error on a variable defined globally?

Question

I’m talking about the variable x.

https://code.sololearn.com/cn93NeiXpUkJ/?ref=app

Answer 1

class thing:
x = 0
def __init__(self,attr):
self.attr = attr
thing.x += 1

Answer 2

Python assumes that the "x" in the class is a class attribute but as it has never been defined, you cannot increase it by 1.

If you want to use the global x, you could write

global x
x += 1

in the class.

Answer 3

x = 0

class thing:
def __init__(self,attr):
self.attr = attr
global x
x += 1

thing1 = thing("t")
print(thing1.attr, x)