Abstract

Python 2.3 added a number of simple date and time types in thedatetime module. There’s no support for parsing strings in variousformats and returning a corresponding instance of one of the types.This PEP proposes adding a family of predefined parsing function forseveral commonly used date and time formats, and a facility for genericparsing.

The types provided by thedatetime module all have.isoformat() and.ctime() methods that return stringrepresentations of a time, and the.strftime() method can be usedto construct new formats. There are a number of additionalcommonly-used formats that would be useful to have as part of thestandard library; this PEP also suggests how to add them.

Input Formats

Useful formats to support include:

• ISO8601
• ARPA/RFC 2822
• 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.)

XXX The PerlParseDate.pm module supports many different input formats,both absolute and relative. Should we try to support them all?

Options:

1. Add functions to thedatetime module:

   importdatetimed=datetime.parse_iso8601("2003-09-15T10:34:54")

2. Add class methods to the various types. There are already variousclass methods such as.now(), so this would be pretty natural.:

   importdatetimed=datetime.date.parse_iso8601("2003-09-15T10:34:54")

3. Add a separate module (possible names: date, date_parse, parse_date)or subpackage (possible names: datetime.parser) containing parsingfunctions:

   importdatetimed=datetime.parser.parse_iso8601("2003-09-15T10:34:54")

Unresolved questions:

• 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 figureit out? (e.g.parse_iso8601("yyyy-mm-dd") returns adate instance,but parsing “yyyy-mm-ddThh:mm:ss” returns adatetime.) Shouldthere be an option to signal an error if a time is provided wherenone is expected, or if no time is provided?
• Anything special required for I18N? For time zones?

Generic Input Parsing

Is a strptime() implementation that returnsdatetime types sufficient?

XXX if yes, describe strptime here. Can the existing pure-Pythonimplementation be easily retargeted?

Output Formats

Not all input formats need to be supported as output formats, because it’spretty trivial to get thestrftime() argument right for simple thingssuch as YYYY/MM/DD. Only complicated formats need to be supported;RFC 2822is currently the only one I can think of.

Options:

1. Provide predefined format strings, so you could write this:

   importdatetimed=datetime.datetime(...)printd.strftime(d.RFC2822_FORMAT)# or datetime.RFC2822_FORMAT?

2. Provide new methods on all the objects:

   d=datetime.datetime(...)printd.rfc822_time()

Relevant functionality in other languages includes thePHP datefunction (Python implementation by Simon Willison athttp://simon.incutio.com/archive/2003/10/07/dateInPython)

References

Other useful links:

http://www.egenix.com/files/python/mxDateTime.htmlhttp://ringmaster.arc.nasa.gov/tools/time_formats.htmlhttp://www.thinkage.ca/english/gcos/expl/b/lib/0tosec.htmlhttps://moin.conectiva.com.br/DateUtil

Copyright

This document has been placed in the public domain.