How do nested functions work in Python?

Question

def maker(n):
    def action(x):
        return x ** n
    return action

f = maker(2)
print(f)
print(f(3))
print(f(4))

g = maker(3)
print(g(3))

print(f(3)) # still remembers 2

Why does the nested function remember the first value 2 even though maker() has returned and exited by the time action() is called?

Answer 1

You can see it as all the variables originating in the parent function being replaced by their actual value inside the child function. This way, there is no need to keep track of the scope of the parent function to make the child function run correctly.

See it as "dynamically creating a function".

def maker(n):
  def action(x):
    return x ** n
  return action

f = maker(2)
--> def action(x):
-->   return x ** 2

This is basic behavior in python, it does the same with multiple assignments.

a = 1
b = 2
a, b = b, a

Python reads this as

a, b = 2, 1

It basically inserts the values before doing anything with them.