In [1]: import datetime

In [2]: datetime.datetime.utcfromtimestamp(0)
Out[2]: datetime.datetime(1970, 1, 1, 0, 0)

In [3]: datetime.datetime.utcfromtimestamp(0).replace(tzinfo=datetime.timezone.utc)
Out[3]: datetime.datetime(1970, 1, 1, 0, 0, tzinfo=datetime.timezone.utc)

datetime.utcfromtimestamp() returns naive datetime.
But some methods assumes naive datetime is localtime. (e.g. datetime.timestamp()).
This is big pitfall for many Pythonistas.

We can't change default behavior for backward compatibility.
How about adding `aware` keyword-only option?

>>> datetime.datetime.utcfromtimestamp(0, aware=True)
datetime.datetime(1970, 1, 1, 0, 0, tzinfo=datetime.timezone.utc)