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pythontype-hinting
RinkyPinku
RinkyPinku

Reputation: 410

Python type hinting - how to hint optional argument whose default is not None?

I am trying to implement PEP-484 in my Python 3 code for practice. While working on the following practice question, which looks like:

def fetch_n(what: str, n="all") -> List[obj]:
    query = "some sql string"
    if n == "all":
        # do the fetching
    elif isinstance(n, int):
        query = query + " LIMIT ?"
        # do the fetching
    else:
        raise ValueError

Is it possible to hint n in the function definition to be -- const str or int? If yes, how to do it?

I read the cheat-sheet and currently I am using from typing import Optional and n: Optional[int] but its not working as desired.

Upvotes: 1

Views: 2379

Answers (1)

Antti Haapala -- Слава Україні
Antti Haapala -- Слава Україні

Reputation: 133849

The Optional[X] is still only a type hint - it means X or None. Perhaps here you'd need an Union instead:

def fetch_n(what: str, n: Union[str, int] = "all") -> List[obj]:
    ...

Upvotes: 5

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