Global and local variable in python with example

Global and local variables in python

In python language, the variable we define and declare outside from the function is known as global variable. That’s a clear meaning that global variable can be accessed inside or outside of a function.

Let’s see by an example

# This function uses global variable a

def cod():

    print (a)

# Global scope

a = "I use codedudle"

cod()

Output:

I use codeddudle

 

Here the variable ‘a’ is defined as the string “I use codedudle” before we call the function cod(). The statement in cod() is the statement of print. So, there is no local a, the value from the global a will be used.

 

What will happen if a variable with the same name is defined inside the scope of function as well then, it will print the value given inside the function only and not the global value.

Lets see by an example

# This function has a variable with

# name same as a.

def cod():

    a = "nice blog."

    print (a)

# Global scope

a = "I use codedudle"

cod()

print (a)

Output:

nice blog.

I use codedudle

Let’s dive a little deeper,  what will happen if we change the value of ‘a’ inside of the function cod()? Will it affect the global ‘a’ as well?

We will see in the following piece of code:

def cod():

    print (a)

       # This program will NOT give an error

       # if we comment below line.

       a = "nice blog"

       print (a)

# Global scope

a = "love to read codedudle"

cod()

print (a)

 

Output:

UnboundLocalError: local variable 'a' referenced before assignment

 

To make the above program work properly, we need to use “global” keyword. We can only need to use the global keyword in a function if we want to do assignments / change them. Now Global is not needed for printing and accessing. Why? Python “assumes” that we want a local variable due to the assignment to ‘a’ inside of cod(), so the first print statement throws this error message. Any variable that is changed or created inside of a function is local, if it hasn’t been declared as a global variable. To tell the Python, that we want to use the global variable, we have to use the keyword “global”, as can be seen in the following example:

# This function modifies the global variable 's'

def cod():

       global a

       print (a)

       a = "best blog for python is codedudle"

       print (a)

# global Scope

a = "Hello world !"

cod()

print (a)

 

Output:

Hello world !

best blog for python is codedudle

best blog for python is codedudle

 

Lets see an brief example

a = 4

# Uses of global because there is no local 'a'

def cod():

       print ('Inside cod() : ', a)

# Variable 'a' is redefined as a local

def dud():

       a = 5

       print ('Inside dud() : ',a)

 

 

# Global scope

print ('global : ',a)

cod()

print ('global : ',a)

dud()

 

Output:

global :  4

Inside cod() :  4

global :  4

Inside dud() :  5

 

In  this article i have Briefly explained about global and local variables. 

Next Article : Packing and Unpacking Arguments in Python

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