The Python Assert Statement

In this article, we’ll examine how to use the assert statement in Python.

In Python, the assert statement is used to validate whether or not a condition is true, using the syntax:

assert

If the condition evaluates to True, the program continues executing as if nothing out of the ordinary happened. However, if the condition evaluates to False, the program terminates with an AssertionError.

>>> assert True

Nothing happens when the code above is executed, since the condition evaluates to True. Alternatively, the condition in the example below evaluates to False:

>>> assert False
Traceback (most recent call last):
  File "", line 1, in 
AssertionError

For added clarity, we can add a custom error message to the assertion output as follows:

>>> assert False, "This is a custom assertion message!"
Traceback (most recent call last):
  File "", line 1, in 
AssertionError: This is a custom assertion message!

The assert statement is useful when we want to check that a variable in our code assumes the correct value and terminate the program if it doesn’t. This helps prevent silent failure modes, which can occur if the program continues executing

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