I meant that it special-cases .microseconds == 0.  If I want to produce
a custom output format using Python Standard Library, I expect to have
to slice, add my own fields and so forth, but I don't expect to need an
"if" to handle a special-case that is there for improving the appearance
to human readers.  That's something I had to do a lot more often when I
worked in Perl.

Even if the cost of changing the definition of isoformat() is too high
at this point, I still wanted to post my code from http://allmydata.org
as an example to other users so that they can use isoformat() safely.