type hint returns NameError: name ‘datetime’ not defined

Question

You need to import datetime, or use a string (remember, it is just an hint).

>>> def f(x: datetime):
...     pass
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'datetime' is not defined
>>> def f(x: 'datetime'):
...     pass
...
>>>
>>> from datetime import datetime
>>> def f(x: datetime):
...     pass
...
>>>

Python 3.7.4

—

UPDATE. For a slightly different version of this issue import __future__.annotations

from __future__ import annotations

def f(dto: Dto):
    pass

class Dto:
    pass

This would otherwise fail in the function reference to the Dto class. Python4 will have this as the default behaviour. For now, the import must be the first statement of the file.

Tested in Python 3.8.10.

See: https://peps.python.org/pep-0563/

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