PEP 321 – Date/Time Parsing and Formatting
- A.M. Kuchling <amk at amk.ca>
- Standards Track
Table of Contents
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
The types provided by the
datetime module all have
.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:
- ARPA/RFC 2822
- 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 Perl ParseDate.pm module supports many different input formats, both absolute and relative. Should we try to support them all?
- Add functions to the
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
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.
dateinstance, 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?
Generic Input Parsing
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; RFC 2822
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.
Last modified: 2022-01-21 11:03:51 GMT