What Is a Global Variable?

• A global variable in Python is a variable with a scope that extends across the entire program. It can be accessed anywhere, inside or outside functions.

Example of a Global Variable:

• Here's a simple example of a global variable:

  python

  x = 'hello world - global'
  
  def myFunction():
      print(x)
  
  myFunction()
  print(x)
  

  • Output:

     

    hello world - global
    hello world - global
    

  • In this example, x is a global variable accessible both inside myFunction() and outside in the main program.

Using the global Keyword:

• When you want to update a global variable inside a function, you need to use the global keyword. Without it, Python will treat the variable as local to the function.

  python

  x = 'hello world - 0'
  
  def myFunction():
      global x
      x = 'hello world - 1'
      print(x)
  
  myFunction()
  print(x)
  

  • Output:

     

    hello world - 1
    hello world - 1
    

  • By declaring x as global inside myFunction(), we ensure the function updates the global variable x rather than creating a new local variable.

Exercises:

1. Global Variable Access:

   • Create a global variable and access it inside a function and outside the function.

     python

     y = 'global variable example'
     
     def exampleFunction():
         print(y)
     
     exampleFunction()
     print(y)
     

2. Updating Global Variable:

   • Write a function that updates a global variable.

     python

     z = 5
     
     def updateGlobalVariable():
         global z
         z = 10
     
     updateGlobalVariable()
     print(z)  # Output: 10
     

Summary:

• Global variables in Python have a scope that spans the entire program. The global keyword is used to modify a global variable inside a function. Practice defining and updating global variables to understand their usage and scope!