Basic Python 27: Global Variable | Local Variable | Nonlocal Variable in Python

Published: 04 October 2022
on channel: Testing Tutorialspoint

Python Global, Local and Nonlocal variables:
--------------------------------------------
Global Variables:
-----------------
A variable declared outside of the function or in global scope is known as a global variable.
This means that a global variable can be accessed inside or outside of the function.
ex:
x = "global"

def foo():
print("x inside:", x)

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

What if you want to change the value of x inside a function?
ex:
x = "global"

def foo():
x = x * 2
print(x)

foo()

error:
UnboundLocalError: local variable 'x' referenced before assignment

Rules of global Keyword:

When we create a variable inside a function, it is local by default.
When we define a variable outside of a function, it is global by default. You don't have to use global keyword.
We use global keyword to read and write a global variable inside a function.
Use of global keyword outside a function has no effect.
ex:
c = 0 # global variable

def add():
global c
c = c + 2 # increment by 2
print("Inside add():", c)

add()
print("In main:", c)

Local Variables:
----------------
A variable declared inside the function's body or in the local scope is known as a local variable.
ex:
def foo():
y = "local"

foo()
print(y)

output:
NameError: name 'y' is not defined

ex2:
def foo():
y = "local"
print(y)

foo()

Global and local variables:
---------------------------
ex:
x = 5

def foo():
x = 10
print("local x:", x)

foo()
print("global x:", x)

Nonlocal Variables:
-------------------
Nonlocal variables are used in nested functions whose local scope is not defined.
This means that the variable can be neither in the local nor the global scope.
We use nonlocal keywords to create nonlocal variables.
ex:
def outer():
x = "local"

def inner():
nonlocal x
x = "nonlocal"
print("inner:", x)

inner()
print("outer:", x)

outer()

output:
inner: nonlocal
outer: nonlocal
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