Python supports closures even when the variable isn't a container. For instance: def add_double(n): x = n * 2 def add(y): retur

Python supports closures even when the variable isn't a container. For instance: def add_double(n): x = n * 2 def add(y): return x + y return add f = add_double(1) f(2) # -> 4 What python versions prior to 3 didn't support is rebinding a variable from an enclosing scope; not because of any fundamental feature of the implementation, but because there was no syntactic way to differentiate between a assigning to a variable in an enclosing scope, and creating a variable in the current scope. So x += 2 is short for x = x + 2, which python interprets as creating a new variable x in the current scope and then trying to access that variable before it's been assigned. Python 3 introduced a syntax to specify that you wanted to assign to a variable from an enclosing scope, the 'nonlocal' keyword. So your example would be: def even(): x = 0 def add(): nonlocal x x += 2 return x return add count = even() count() # → 2 count() # → 4