Can I trust mktime ?

[Martin von Loewis]

Tim Howarth <tim at worthy.demon.co.uk> writes:

> To find the date in 4 months time I've added to the months element of a
> list copy of a localtime tuple.
> 
> (Which obvioulsy means months can be >12.)
> 
> Is converting this to a time() value with mktime then reading back with
> localtime() considered correct/safe ?

On a POSIX system, that might be safe. The mktime(3) documentation of
glibc says

# If structure members are outside their legal interval, they will be
# normalized (so that, e.g., 40 October is changed into 9 November).

I haven't actually verified that this is the POSIX semantics of the
function, though. In any case, Python delegates this call to the C
library, so you are left to the mercy of the C library's implementors.

HTH,
Martin