Convert timestamps with offset to datetime obj using strptime

问题:

I am trying to convert time-stamps of the format "2012-07-24T23:14:29-07:00" to datetime objects in python using strptime method. The problem is with the time offset at the end(-07:00). Without the offset i can successfully do

time_str = "2012-07-24T23:14:29"  time_obj=datetime.datetime.strptime(time_str,'%Y-%m-%dT%H:%M:%S') 

But with the offset i tried

time_str = "2012-07-24T23:14:29-07:00"  time_obj=datetime.datetime.strptime(time_str,'%Y-%m-%dT%H:%M:%S-%z'). 

But it gives a Value error saying "z" is a bad directive.

Any ideas for a work around?

回答1:

The Python 2 strptime() function indeed does not support the %z format for timezones (because the underlying time.strptime() function doesn't support it). You have two options:

• Ignore the timezone when parsing with strptime:

  time_obj = datetime.datetime.strptime(time_str[:19], '%Y-%m-%dT%H:%M:%S') 

• use the dateutil module, it's parse function does deal with timezones:

  from dateutil.parser import parse time_obj = parse(time_str) 

Quick demo on the command prompt:

>>> from dateutil.parser import parse >>> parse("2012-07-24T23:14:29-07:00") datetime.datetime(2012, 7, 24, 23, 14, 29, tzinfo=tzoffset(None, -25200)) 

You could also upgrade to Python 3.2 or newer, where timezone support has been improved to the point that %z would work, provided you remove the last : from the input, and the - from before the %z:

>>> import datetime >>> time_str = "2012-07-24T23:14:29-07:00" >>> datetime.datetime.strptime(time_str, '%Y-%m-%dT%H:%M:%S%z') Traceback (most recent call last):   File "", line 1, in    File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python3.4/_strptime.py", line 500, in _strptime_datetime     tt, fraction = _strptime(data_string, format)   File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python3.4/_strptime.py", line 337, in _strptime     (data_string, format)) ValueError: time data '2012-07-24T23:14:29-07:00' does not match format '%Y-%m-%dT%H:%M:%S%z' >>> ''.join(time_str.rsplit(':', 1)) '2012-07-24T23:14:29-0700' >>> datetime.datetime.strptime(''.join(time_str.rsplit(':', 1)), '%Y-%m-%dT%H:%M:%S%z') datetime.datetime(2012, 7, 24, 23, 14, 29, tzinfo=datetime.timezone(datetime.timedelta(-1, 61200))) 

回答2:

In Python 3.2+:

from datetime import datetime  time_str = "2012-07-24T23:14:29-0700" dt_aware = datetime.strptime(time_str, '%Y-%m-%dT%H:%M:%S%z') print(dt_aware.isoformat('T')) # -> 2012-07-24T23:14:29-07:00 

Note: it doesn't support : in the -0700 part (both formats are allowed by rfc 3339). See datetime: add ability to parse RFC 3339 dates and times.

On older Python versions such as Python 2.7, you could parse the utc offset manually:

from datetime import datetime  time_str = "2012-07-24T23:14:29-0700" # split the utc offset part naive_time_str, offset_str = time_str[:-5], time_str[-5:] # parse the naive date/time part naive_dt = datetime.strptime(naive_time_str, '%Y-%m-%dT%H:%M:%S') # parse the utc offset offset = int(offset_str[-4:-2])*60 + int(offset_str[-2:]) if offset_str[0] == "-":    offset = -offset dt = naive_dt.replace(tzinfo=FixedOffset(offset)) print(dt.isoformat('T')) 

where FixedOffset class is defined here.

回答3:

ValueError: 'z' is a bad directive in format...

(note: I have to stick to python 2.7 in my case)

I have had a similar problem parsing commit dates from the output of git log --date=iso8601 which actually isn't the ISO8601 format (hence the addition of --date=iso8601-strict in a later version).

Since I am using django I can leverage the utilities there.

https://github.com/django/django/blob/master/django/utils/dateparse.py

>>> from django.utils.dateparse import parse_datetime >>> parse_datetime('2013-07-23T15:10:59.342107+01:00') datetime.datetime(2013, 7, 23, 15, 10, 59, 342107, tzinfo=+0100) 

Instead of strptime you could use your own regular expression.

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