How to declare a global variable in Python

In this tutorial, we will learn how to declare a global Variable in Python Program.

What is a Global Variable?

The global variables are the ones that are available both within and outside of any function, provided they are defined outside a function which is a global scope. Let's explore the creation of a global variable.

In this example, we will define and access a global variable.

Example:

Output:

Inside the defined function the string is: Declaring the Global Variable Outside the defined function the string is: Declaring the Global Variable 

Accessing the Global Variable

The variable var is accessed both within and outside the function func(), and since it is declared in the global scope, it is designated as a global variable.

Since we have not created local variables, the value of the global variable will be applied; however, we must ensure that the names of the local and global variables match.

What if a variable with the same identifier is initialized globally and inside a defined function? What will occur if we modify the value of a variable within the function func()? The problem is whether changing the local variable will change the global variable or, conversely, changing the global variable will change the local variable. The following example of code is used to evaluate it:

Example:

Output:

The local scope variable is: Global Variable The local scope variable is: I am leaning Python 

Suppose a certain variable, having the name just as given to the variable in the global scope, is declared inside the function's local scope. In that case, it will only show the value provided within the defined function but not the global value.

Changing Global Variable inside the Local Scope

What would happen if we attempted to alter the value of a variable defined in the global scope inside the function? Let's examine it with the help of the example below.

Example:

Output:

 4 def func(): ----> 5 var = var + "Global Variable" 6 print( "Inside the defined function", var ) 

UnboundLocalError: local variable 'var' referenced before assignment

We must include the "global" Python keyword for the preceding application to run. Let us now study the global variable.

Global Keyword

When assigning values to or changing the variables declared in global scope within a function, we must use the global Python keyword. The keyword is not required to display or access a global scope variable. Since we declared var inside the function func(), the Python interpreter "assumes" that we desire a local variable, which is why the first sentence raises the error. It is considered local if a variable is modified or declared inside a function without being declared a global variable using the global keyword. The following example demonstrates how to employ the keyword "global" to instruct the Python interpreter that we wish to access the global variable.

Example:

Output:

Inside the defined function: Python Tutorial Global Variable Outside the function: Python Tutorial Global Variable 

Example to Show Use of Local and Global Variables

Example

Output:

global value of variable: 10 Inside the first function: 10 global value of variable: 10 Inside the second function: 15 global value of variable: 10 Inside the third function: 13 global value of variable: 13