Core Python Programming

10.7. Assertions

Assertions are diagnostic predicates which must evaluate to Boolean true; otherwise, an exception is raised to indicate that the expression is false. These work similarly to the assert macros which are part of the C language preprocessor, but in Python these are run-time constructs (as opposed to pre-compile directives).

If you are new to the concept of assertions, no problem. The easiest way to think of an assertion is to liken it to a raise-if statement (or to be more accurate, a raise-if-not statement). An expression is tested, and if the result comes up false, an exception is raised.

Assertions are carried out by the assert statement, the newest keyword to Python, introduced in version 1.5.

10.7.1. assert Statement

The ...