Interval literals with year/months have different number of seconds w.r.t. Python

[dvarrazzo]

select '-1 year -2 mons +3 days -04:05:06'::interval doesn't return the correct value in Python

[dvarrazzo]

Not a bug in the sign as I imagined: postgres adds 6 hours every year or every 12 months (but not 3 hours for 6 months or something like that).

I think it makes more sense to apply the same conversion, so that extract(epoch from interval) matches the timedelta.total_seconds() of the returned object.

Also note that these intervals are pretty specific: they are not obtained by the difference between timestamps, which is always expressed in months. Also, there is no problem of roundtrips because with Python intervals you can't express months and years.

[dvarrazzo]

Not closing now this ticket. This behaviour has been "broken" this way forever (I thought it was broken in the reimplementation for #536).