CODEWITHSUNDEEP
pythonpython-3.xtype-hintingmypy
ryche
ryche

Reputation: 2094

mypy: Value of type "Optional[Mapping[Any, Any]]" is not indexable

Why does mypy say that the value returned by the fetch_one method of the databases library is not indexable? What should I do in this case to resolve this error?

async def get_reaction_by_name(name: str, user_id: str) -> Optional[Mapping[Any, Any]]:
    query = reactions.select().where(
        (reactions.c.name == name) & (reactions.c.user_id == user_id)
    )
    return await database.fetch_one(query)

...

reaction = await get_reaction_by_name(name=name, user_id=user_id)
reaction["name"]

# mypy: Value of type "Optional[Mapping[Any, Any]]" is not indexable

Upvotes: 0

Views: 2013

Answers (1)

Azat Ibrakov
Azat Ibrakov

Reputation: 10989

What mypy says us is that since function returns Optional[...] before treating its result as a ... (Mapping[Any, Any] in given snippet) we should check whether it's not a None like

reaction = await get_reaction_by_name(name=name, user_id=user_id)
if reaction is not None:
    reaction["name"]

Upvotes: 2

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