|Title:||Date/Time Parsing and Formatting|
|Last-Modified:||2007-06-19 04:20:07 +0000 (Tue, 19 Jun 2007)|
|Author:||A.M. Kuchling <amk at amk.ca>|
Python 2.3 added a number of simple date and time types in the datetime module. There's no support for parsing strings in various formats and returning a corresponding instance of one of the types. This PEP proposes adding a family of predefined parsing function for several commonly used date and time formats, and a facility for generic parsing.
The types provided by the datetime module all have .isoformat() and .ctime() methods that return string representations of a time, and the .strftime() method can be used to construct new formats. There are a number of additional commonly-used formats that would be useful to have as part of the standard library; this PEP also suggests how to add them.
Useful formats to support include:
- ISO8601 
- ARPA/RFC2822 
- ctime 
- Formats commonly written by humans such as the American "MM/DD/YYYY", the European "YYYY/MM/DD", and variants such as "DD-Month-YYYY".
- CVS-style or tar-style dates ("tomorrow", "12 hours ago", etc.)
Add functions to the datetime module:
import datetime d = datetime.parse_iso8601("2003-09-15T10:34:54")
Add class methods to the various types. There are already various class methods such as .now(), so this would be pretty natural.:
import datetime d = datetime.date.parse_iso8601("2003-09-15T10:34:54")
Add a separate module (possible names: date, date_parse, parse_date) or subpackage (possible names: datetime.parser) containing parsing functions:
import datetime d = datetime.parser.parse_iso8601("2003-09-15T10:34:54")
- Naming convention to use.
- What exception to raise on errors? ValueError, or a specialized exception?
- Should you know what type you're expecting, or should the parsing figure it out? (e.g. parse_iso8601("yyyy-mm-dd") returns a date instance, but parsing "yyyy-mm-ddThh:mm:ss" returns a datetime.) Should there be an option to signal an error if a time is provided where none is expected, or if no time is provided?
- Anything special required for I18N? For time zones?
Is a strptime() implementation that returns datetime types sufficient?
XXX if yes, describe strptime here. Can the existing pure-Python implementation be easily retargeted?
Not all input formats need to be supported as output formats, because it's pretty trivial to get the strftime() argument right for simple things such as YYYY/MM/DD. Only complicated formats need to be supported; RFC2822 is currently the only one I can think of.
Provide predefined format strings, so you could write this:
import datetime d = datetime.datetime(...) print d.strftime(d.RFC2822_FORMAT) # or datetime.RFC2822_FORMAT?
Provide new methods on all the objects:
d = datetime.datetime(...) print d.rfc822_time()
Relevant functionality in other languages includes the PHP date  function (Python implementation by Simon Willison at http://simon.incutio.com/archive/2003/10/07/dateInPython)
Other useful links:
http://www.egenix.com/files/python/mxDateTime.html http://ringmaster.arc.nasa.gov/tools/time_formats.html http://www.thinkage.ca/english/gcos/expl/b/lib/0tosec.html https://moin.conectiva.com.br/DateUtil
This document has been placed in the public domain.