Python Scope

Local and global

A variable created inside a function is local to it. Variables created at the top level of a file are global.

x = "global"

def show():
    x = "local"
    print("inside:", x)

show()
print("outside:", x)

inside: local
outside: global

Python looks names up in order: Local → Enclosing function → Global → Built-in (the LEGB rule).

Changing outer variables

Assigning inside a function creates a new local variable. To change a global, declare it with global; to change a variable from an enclosing function, use nonlocal.

count = 0

def increment():
    global count
    count += 1

increment()
increment()
print(count)

def make_counter():
    n = 0
    def step():
        nonlocal n
        n += 1
        return n
    return step

counter = make_counter()
counter()
print(counter())

2
2

Prefer returning values over modifying globals — it keeps functions predictable.

Closures

An inner function remembers the variables of the function that created it:

def multiplier(factor):
    def multiply(x):
        return x * factor
    return multiply

double = multiplier(2)
triple = multiplier(3)
print(double(5), triple(5))

10 15