Python Variable Scope

Local Scope

A variable created inside a function is local to that function — it exists only while the function runs and is not visible outside it. Each function call gets its own fresh set of local variables.

def greet():
    message = "Hello!"   # local to greet()
    print(message)

greet()
print(message)   # NameError: message is not defined here

Global Scope

A variable created outside of any function, at the top level of your script, is global — it can be read from anywhere, including inside functions, without any special keyword.

site_name = "MyInternships"   # global

def show_name():
    print(site_name)   # can read the global directly

show_name()

The global Keyword

Reading a global variable inside a function works automatically, but modifying it requires the global keyword — otherwise Python assumes you are creating a brand new local variable with the same name.

counter = 0

def increment():
    global counter
    counter += 1

increment()
increment()
print(counter)   # 2

The nonlocal Keyword

nonlocal is used inside a nested function to modify a variable that belongs to its enclosing (outer) function, without making it fully global. It is the key building block behind closures.

def outer():
    count = 0
    def inner():
        nonlocal count
        count += 1
        return count
    print(inner())   # 1
    print(inner())   # 2

outer()

The LEGB Rule

When Python looks up a name, it searches four scopes in this exact order and stops at the first match: Local, Enclosing, Global, Built-in.