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

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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