Python's free variables behaviour with inner classes

This is the challenge:

x = 11
def foo1():
  x = 2
  class foo:
    print(x)
foo1()  # prints 2

x = 11
def foo2():
  x = 2
  class foo:
    print(x)
    x += 1
foo2()  # prints 11

What is the explanation of this behaviour? Anyone?