Modify variable in scope of a function in another function in the same scope (Python)

I have a variable a whose scope is in function f().
There is another function b() in the scope of f(), where variable a is getting modified. How can I make sure the variable gets modified in function b() and is reflected correctly in the scope of function f()?

def f():
      a = 1
      def b():
             global a
             a = 2
      b()
      print(a)
 
f()

>>> 1  # expected is 2