Occasionally, we want to be able to modify a global variable from within a more specific context. In this situation, Python provides us with the global keyword.

Python Global keyword:

In this tutorial, we’ll see how to use the global keyword in Python.

If we would like one of our functions to have the side effect of changing or creating a global variable, we can utilize the global statement.

This isn’t something that we’ll use all that often since it is better to keep the global state to a minimum as we start working on larger and more complex programs. But it is useful now and then.

Let’s modify scopes.py so that we can change the global y variable from within our set_x function:

scopes.py
y = 10

def set_x(y):
    print("Inner y:", y)
    x = y
    global y
    y = x

set_x(20)
print("Outer y:", y)

If we run this, we should see the following:

Terminal
File "<input>", line 6
SyntaxError: name 'y' is parameter and global

It’s important to know that we can’t utilize the global statement if we have a parameter with the same name. Let’s change our parameter to be z before running this again:

scopes.py
y = 10

def set_x(z):
    x = z
    global y
    global a
    y = x
    a = 7

print("y Before set_x:", y)
set_x(20)
print("y After set_x:", y)
print("a After set_x:", a)

We’ve also created a global variable from within our set_x function called a. This variable won’t be available before the first time that set_x is called, but we should be able to print it after we’ve called our function for the first time. Let’s run scopes.py again:

Terminal
y Before set_x: 10
y After set_x: 20
a After set_x: 7

This example shows how potentially confusing using global can be. We have a function called set_x that will change the global state for the variable y.

Someone who didn’t write this code could be completely confused as to why the value of the variable y that they’ve been working with was changed right out from under them. So Keep this in mind when considering whether or not it’s a good idea to use the global statement.

References:

Happy Learning 🙂

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