Part of the problem here is that the strings usually used to represent timezones are not actually unique. "EST" only means "America/New_York" to people in North America. This is a limitation in the C time API, and the Python solution is… to add full tz features in some future version any day now, if anyone is willing to write the PEP.
You can format and parse a timezone as an offset, but that loses daylight savings/summer time information (e.g., you can't distinguish "America/Phoenix" from "America/Los_Angeles" in the summer). You can format a timezone as a 3-letter abbreviation, but you can't parse it back from that.
If you want something that's fuzzy and ambiguous but usually what you want, you need a third-party library like dateutil.
If you want something that's actually unambiguous, just append the actual tz name to the local datetime string yourself, and split it back off on the other end:
d = datetime.datetime.now(pytz.timezone("America/New_York"))
dtz_string = d.strftime(fmt) + ' ' + "America/New_York"
d_string, tz_string = dtz_string.rsplit(' ', 1)
d2 = datetime.datetime.strptime(d_string, fmt)
tz2 = pytz.timezone(tz_string)
print d2.strftime(fmt) + ' ' + tz_string
Or… halfway between those two, you're already using the pytz library, which can parse (according to some arbitrary but well-defined disambiguation rules) formats like "EST". So, if you really want to, you can leave the %Z in on the formatting side, then pull it off and parse it with pytz.timezone()before passing the rest to strptime.