See the following code:
import datetime import pytz fmt = '%Y-%m-%d %H:%M:%S %Z' d = datetime.datetime.now(pytz.timezone("America/New_York")) d_string = d.strftime(fmt) d2 = datetime.datetime.strptime(d_string, fmt) print d_string print d2.strftime(fmt)
the output is
2013-02-07 17:42:31 EST 2013-02-07 17:42:31
The timezone information simply got lost in the translation.
If I switch '%Z' to '%z', I get
ValueError: 'z' is a bad directive in format '%Y-%m-%d %H:%M:%S %z'
I know I can use python-dateutil
, but I just found it bizzare that I can't achieve this simple feature in datetime and have to introduce more dependency?
Python time strptime() MethodThe format parameter uses the same directives as those used by strftime(); it defaults to "%a %b %d %H:%M:%S %Y" which matches the formatting returned by ctime(). If string cannot be parsed according to format, or if it has excess data after parsing, ValueError is raised.
When the %z directive is provided to the strptime() method, an aware datetime object will be produced. The tzinfo of the result will be set to a timezone instance.
Python time strptime() function The strptime() function in Python is used to format and return a string representation of date and time. It takes in the date, time, or both as an input, and parses it according to the directives given to it.
strptime is short for "parse time" where strftime is for "formatting time". That is, strptime is the opposite of strftime though they use, conveniently, the same formatting specification.
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 dtz_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
.
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