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Python Global Variables: How Do They Differ From the Local Ones?

Reading time 2 min
Published Feb 13, 2020
Updated Feb 13, 2020

TL;DR – Python global variables are declared outside a function and can be accessed anywhere in the code.

The difference between local and global variables in Python

In the example below, you can see two variables declared – bit and bdg:

def f():
    bit = "BitDegree"
    print (bit)

bdg = "BitDegree"
print (bdg)

While both have the same value assigned, they are declared and used differently:

  • bit is declared within the function. This makes it a local variable. Its scope is the body of the function – it cannot be used anywhere else.
  • bdg is declared outside of the function – this makes it global. You can use Python global variables anywhere in the code.
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How to use global variables in Python

When declaring global variables in Python, you can use the same names you have already used for local variables in the same code – this will not cause any issues because of the scope difference:

  • If you use the variable within the function, it will prefer the local variable by default:
  • Example
    pizza = "Pepperoni"
    def f():
        pizza = "Hawaii"
        print (pizza)
  • If you use the variable anywhere else in the code, you will get the value of the global variable:
  • Example
    pizza = "Pepperoni"
    def f():
        pizza = "Hawaii"
    print (pizza)

You can also create local variables by modifying previously defined Python global variables inside the function by using the keyword global:

bdg = 1000

def f():
    global bdg
    bdg = bdg + 500

Python global variables: useful tips

  • You can change the value of a Python global variable by simply assigning it a new value (redeclaring).
  • To delete a variable, use the keyword del. Trying to use a deleted variable will cause an error to fire.

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