2013/11/5 Alexander Belopolsky <report@bugs.python.org>:
> +1 on adding an option to isoformat().  We already have an optional <sep> argument, so the symmetry with __str__ is not complete.  To make this option more useful, rather than implementing always_emit_microseconds=False flag, I would add a keyword argument 'precision' that would take ('hour'|'minute'|'second'|millisecond'|'microsecond') value.

Hour precision is not part of the ISO 8601 standard.

"resolution" is maybe a better name for the new parameter than "precision":
http://www.python.org/dev/peps/pep-0418/#glossary

The new parameter should be added to datetime.datetime.isoformat() but
also datetime.time.isoformat().