Python Types: Optional Can Mean Mandatory | by Marcin Kozak | Nov, 2023

PYTHON PROGRAMMING

Learn to keep away from a frequent misuse and misunderstanding of typing.Non-obligatory.

In keeping with the Python documentation, typing.Non-obligatory is a helpful method to point out that an object will be None. It’s a concise and chic method to specific this idea, however is it additionally crystal clear?

Let me rephrase this query: Once you see the phrase “elective” in a Python context, what do you assume it means? Think about you see an argument known as x that has the kind of Non-obligatory[int]. The int half is somewhat clear, as most probably signifies an integer, however what does Non-obligatory imply? What’s your first thought?

Let’s take into account the next two choices:

1. I don’t have to offer a worth of x as a result of it’s elective.
2. x worth will be both int or None.

If you understand Python kind hinting nicely sufficient, you understand choice 2 is appropriate. However if you don’t… Possibly I’m unsuitable, however I can’t think about any one that doesn’t know Python selecting choice 2. It’s choice 1 that appears to make most sense. Once I see data that one thing is elective, I feel that… nicely, that it’s elective…

This challenge results in a frequent misuse of the typing.Non-obligatory kind. This text goals to make clear this misuse and information you in the direction of the proper understanding of this sort.

These three kind hints are equal:

from typing import Non-obligatory, Union
x: Union[str, None]
x: Non-obligatory[str]
x: str | None

Every of them conveys the identical data: that x will be both a string or None. Whereas completely legitimate, the primary one (Union[str, None]) represents the early levels of kind hinting in Python: it was the preliminary strategy, nevertheless it’s not essentially the popular methodology these days. Then, Non-obligatory was added to the typing module, offering a extra concise and easy method to specific this idea. In keeping with the mypy documentation:

You should utilize the Optional kind modifier to outline a sort variant that enables None, similar to Non-obligatory[int] (Non-obligatory[X] is the popular shorthand for Union[X, None]).