Best way of using Python Global Variables

  • Reading time:5 mins read

What is a Python global variable?

In programming, a variable is simply a memory location that is used to store values.

Variables are classified in accordance with their type and scope within a program. Variables based on the scope can be classified into local variables and global variables.

 

How to use a Python global variable?

The scope of a variable in a program depends on whether it is declared within or outside a function. Using two simple functions below we are going to learn about Python global variables.

 

python global variable

 

In the code below we have two functions: the say_hi() function that takes the name of the animal variable and later prints the variable with ‘says HI!’ afterwards.

The second function is called change_animal() which is basically designed to redeclare the animal variable and assign it a new value.

 

Example 1

Now if we run the first function and leave out the second function, we’re going to get the output in the terminal that says ‘says HI !’.

This is because we have the animal variable declared as the global variable that we have referenced within the function.

 

 

If we uncomment the second function by just looking at the function one might speculate that the variable animal is going to be reassigned to ‘leopard’.So we should get ‘leopard says HI’.

 

python global variable

 

However, we do not get such an output since the variable animal that is declared within the change_animal() function is a local variable.

Although it has the same name as the initial animal variable that is declared at the beginning of the program the variable goes into garbage collection since it is not used by the program.

 

 

The function ‘say_hi’ won’t know that anything has happened and we will still get the animal variable as the elephant.

We can change the local variable to interact with the global variable by adding a short command inside the ‘change_animal’ function.

 

python global variable

Example 2

However, we need to be careful when using global variables this way in our code and make sure it is too difficult to understand what is going on in the program.

In this case, if we wanted to use the ‘change_animal’ function to we could do so by writing the word global and then giving it the name of the variable. If we now run the function it will actually change the value of the animal variable.

 

 

Now that the animal variable declared within the ‘change_animal’ function is actually a global function declaring it with a different value affects the animal variable declared in the global scope.

Generally, any variable declared in the main part of the body on the far left is considered a global variable. And any variable declared within a defined function unless the name global precedes it is a local variable.

Local variables are only usable within the function in which they are defined. Any attempt to use them outside that function results in an error.

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