How to check if a variable exists in Python

You can easily check if a variable exists in Python in either local or global scope.

To check if a variable exists in the global scope, verify the name of the variable as a string between quotes and use the in operator using the globals() function.

To check if a variable exists in the local scope, you also verify the name of the variable as a string and check it against the locals() function.

Paste the code below in exists.py file and run on your terminal python exists.py.

my_phrase = 'Hello World'

def prints_the_argument(phrase):
    print(phrase)

    if "my_phrase" in globals():
        print("my_phrase exists globally")

    if "my_phrase" in locals():
        print("my_phrase exists locally")

    if "phrase" in globals():
        print("phrase exists globally")

    if "phrase" in locals():
        print("phrase exists locally")

prints_the_argument('Hello World')

You should see the output below.

Hello World
my_phrase exists globally
phrase exists locally

Notice how my_phrase is in the global scope, but not in local, while phrase exists in the local scope, but not in global.

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