[issue33812] Different behavior between datetime.py and its C accelerator

[Tim Peters]

Tim Peters <tim at python.org> added the comment:

I copy/pasted the definitions of "aware" and "naive" from the docs.  Your TZ's .utcoffset() returns None, so, yes, any datetime using an instance of that for its tzinfo is naive.

In

print(datetime(2000,1,1).astimezone(timezone.utc))

the docs for astimezone say, in part,

"""
If self is naive (self.tzinfo is None), it is presumed to represent time in the system timezone.
"""

So it converted your naive time (viewed as being in your system - EDT - time zone) to UTC.

That appears to be using a different definition of "naive" (looking only at whether self.tzinfo is None).

The original datetime.py certainly didn't do that ...

"""
def astimezone(self, tz):
    if not isinstance(tz, tzinfo):
        raise TypeError("tz argument must be an instance of tzinfo")
    mytz = self.tzinfo
    if mytz is None:
        raise ValueError("astimezone() requires an aware datetime")

    if tz is mytz:
        return self

    # Convert self to UTC, and attach the new time zone object.
    myoffset = self.utcoffset()
    if myoffset is None:
        raise ValueError("astimezone() requires an aware datetime")
"""

So it originally used the definition I quoted first.  The "sometimes pretend it's local time anyway" twist appeared to get added here:

https://github.com/python/cpython/commit/fdc860f3106b59ec908e0b605e51a1607ea2ff4b

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<https://bugs.python.org/issue33812>
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