CODEWITHSUNDEEP
pythonpython-typing
Keisuke Nagakawa 永川 圭介
Keisuke Nagakawa 永川 圭介

Reputation: 1125

Type hint for a list with 0 or more items

I have a list which can have one or more items:

a_list = ["apple"]

But it can also be empty:

a_list = []

In this case, which of List[str] and List[Optional[str]] is the appropriate type-hint for this variable and why?

Upvotes: 7

Views: 7238

Answers (2)

Marko
Marko

Reputation: 45

As of python 3.10 list will do just fine:

# 3.10 and above
my_list: list[str] = []

# earlier versions of python
from typing import List
ma_list: List[str] = []

Upvotes: 1

chepner
chepner

Reputation: 532303

List[str] includes all lists of strings, including the empty list. (From a typing perspective, an empty list of type List[str] is distinct from an empty list of type List[int]).

Optional[str] is shorthand for Union[None, str], so List[Optional[str]] is the type of lists that can contain str values and Nones, not the type of list that may or may not have a str value.

Upvotes: 11

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