Question: I have a function which returns a psycopg2 connection, if a connection can be established. So the return type should be Optional[psycopg2.connection], or psycopg2.connection | None. However I am unable to import psycopg2.connection at runtime. I've tried the workaround mentioned in How can I import type-definitions from a typeshed stub-file? but that gives me this mypy error: Single overload definition, multiple required. Here's my code import psycopg2 from typing import Optional, TYPE_CHECKING, overload if TYPE_CHECKING: from psycopg2 import connection @overload def get_connection() -> Optional[connection]: ... # Make DB error logging less spammy has_logged_error = False def get_connection(): try: conn = psycopg2.connect( dbname=settings.db_name, user=settings.db_user, password=settings.db_password, host=settings.db_host, port=settings.db_port, ) return conn except Exception as e: global has_logged_error if not has_logged_error: logger.error(f"Error connecting to DB: {e}") has_logged_error = True return 

Answer: The question you linked proposes some extremely dirty hack which doesn't seem to work any more. There is absolutely no need for it under such simple circumstances. Moreover, to be honest, I cannot reproduce that solution on any mypy version starting from 0.800 (old enough, given that the linked answer is recent), so that perhaps never worked. I reduced your code samples to contain only minimal return for the sake of readability. Variant 1: use conditional import and string annotation import psycopg2 from typing import Optional, TYPE_CHECKING if TYPE_CHECKING: from psycopg2 import connection def get_connection() -> Optional['connection']: return psycopg2.connect(...)  This is simple: mypy known what connection is (defined in stubs); runtime does not try to learn something about connection because it sees simply a string. Variant 2: use conditional import and annotations future from __future__ import annotations import psycopg2 from typing import Optional, TYPE_CHECKING if TYPE_CHECKING: from psycopg2 import connection def get_connection() -> Optional[connection]: return psycopg2.connect(...)  Docs for future imports. This is very similar to direct string usage, but looks nicer and is more convenient, IMO. Variant 3: use string annotation, but avoid conditional import import psycopg2 from typing import Optional def get_connection() -> Optional['psycopg2.connection']: return psycopg2.connect(...)  Variant 4: use annotations future, but avoid conditional import from __future__ import annotations import psycopg2 from typing import Optional def get_connection() -> Optional[psycopg2.connection]: return psycopg2.connect(...)  Variants 3 and 4 do not expose that connection is stub-only, hiding it as implementation detail. You may prefer to state that explicitly - then use 1 or 2. Modification to use current features This is my favorite. Union syntax is valid in python 3.10+, so if you use an older one - you may want to stick with Optional as described above for consistency. However, annotations future-import makes this expression effectively a string, so if your tools do not perform any runtime typing introspection - you can still use pipe union syntax on older versions. Just be aware that typing.get_type_hints and similar utilities will fail with this syntax on python before 3.10. from __future__ import annotations import psycopg2 def get_connection() -> psycopg2.connection | None: return psycopg2.connect(...)