Handle negative timestamps in from_timestamp - #3026

I don't think you need a platform check — the issue is fromtimestamp itself, which raises OSError [Errno 22] on Windows for pre-1970 values, even with tz=utc. Building the datetime from a timedelta sidesteps it and gives the same result:

return (dt.datetime(1970, 1, 1, tzinfo=dt.timezone.utc) + dt.timedelta(seconds=value)).replace(tzinfo=None)

Both of your new cases pass with it on Windows (py3.12): -627296460 → 1950-02-14 14:59:00, and -627296459.42 → 1950-02-14 14:59:00.580000.

Nice. But I suppose this comes with a performance penalty, so I'd rather do it only when necessary.
Maybe we could try this in the except OSError path? And on Windows only.

Good call, that keeps the fast path untouched. On Windows it's fromtimestamp itself that raises the OSError, so the except branch scopes it exactly where it's needed with no explicit platform check:

try:
    return dt.datetime.fromtimestamp(value, tz=dt.timezone.utc).replace(tzinfo=None)
except OSError:
    return (dt.datetime(1970, 1, 1, tzinfo=dt.timezone.utc) + dt.timedelta(seconds=value)).replace(tzinfo=None)

Both new cases pass here on Windows (py3.12): -627296460 → 1950-02-14 14:59:00 and -627296459.42 → 1950-02-14 14:59:00.580000, and the positive timestamps never enter the except branch so there's no penalty on the common path.

It revealed a little more complicated as there are cases where OSError is raised on value overflow. This happens at least on Linux. So I had to catch OverflowError in the OSError handling code.

This implies a slight perf regression on out-of-range values, since we get en OSError, then try again with the timedelta method, only to get an OverflowError from timedelta.

It seems acceptable to penalize an error path for a wider feature coverage.

The code looks ugly, but oh well.