On twitter, someone asked about a weird difference in the error messages fromdatetime.fromtimestamp() when called with a timestamp that falls on 10000-01-01 when compared to 10000-01-02. Compare:

$ TZ=UTC python -c "from datetime import *; datetime.fromtimestamp(253402300799 + 1)"Traceback (most recent call last):  File "<string>", line 1, in <module>ValueError: year 0 is out of range$ TZ=UTC python -c "from datetime import *; datetime.fromtimestamp(253402300799 + 1 + 24 * 3600)"Traceback (most recent call last):  File "<string>", line 1, in <module>ValueError: year 10000 is out of range

Turns out that this is because in the localtime-specific implementation ofdatetime.fromtimestamp in_datetimemodule.c, there's an unchecked error condition when callingutc_to_seconds, which fails with-1.

As a practical matter, this always results in basically the same error anyway, since in all situations whereresult_seconds gets set to-1 the subsequent calculations fail anyway, and the only difference is that the error message has a slightly different form, but we may as well fix this.