113 – Constant variables

There is no way to create a true constant in Python. Instead, you can use other mechanisms to signal to people that some values shouldn’t change.

PEP 8 establishes the convention that if a variable has its name written in ALL_UPPERCASE, then that’s a constant and you shouldn’t modify its value:

PI = 3.1415

Additionally, the module typing has the annotation Final that you can use to indicate to type checkers that a given name shouldn’t be reassigned to. Final is a generic that takes the true type of the variable inside square brackets []:

PI: Final[float] = 3.1415