150 lines
4.3 KiB
ReStructuredText
150 lines
4.3 KiB
ReStructuredText
PEP: 321
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Title: Date/Time Parsing and Formatting
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Version: $Revision$
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Last-Modified: $Date$
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Author: A.M. Kuchling <amk@amk.ca>
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Status: Withdrawn
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Type: Standards Track
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Content-Type: text/x-rst
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Created: 16-Sep-2003
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Python-Version: 2.4
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Post-History:
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Abstract
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========
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Python 2.3 added a number of simple date and time types in the
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``datetime`` module. There's no support for parsing strings in various
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formats and returning a corresponding instance of one of the types.
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This PEP proposes adding a family of predefined parsing function for
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several commonly used date and time formats, and a facility for generic
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parsing.
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The types provided by the ``datetime`` module all have
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``.isoformat()`` and ``.ctime()`` methods that return string
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representations of a time, and the ``.strftime()`` method can be used
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to construct new formats. There are a number of additional
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commonly-used formats that would be useful to have as part of the
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standard library; this PEP also suggests how to add them.
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Input Formats
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=======================
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Useful formats to support include:
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* `ISO8601`_
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* ARPA/:rfc:`2822`
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* `ctime`_
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* Formats commonly written by humans such as the American
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"MM/DD/YYYY", the European "YYYY/MM/DD", and variants such as
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"DD-Month-YYYY".
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* CVS-style or tar-style dates ("tomorrow", "12 hours ago", etc.)
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XXX The Perl `ParseDate.pm`_ module supports many different input formats,
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both absolute and relative. Should we try to support them all?
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Options:
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1) Add functions to the ``datetime`` module::
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import datetime
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d = datetime.parse_iso8601("2003-09-15T10:34:54")
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2) Add class methods to the various types. There are already various
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class methods such as ``.now()``, so this would be pretty natural.::
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import datetime
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d = datetime.date.parse_iso8601("2003-09-15T10:34:54")
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3) Add a separate module (possible names: date, date_parse, parse_date)
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or subpackage (possible names: datetime.parser) containing parsing
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functions::
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import datetime
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d = datetime.parser.parse_iso8601("2003-09-15T10:34:54")
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Unresolved questions:
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* Naming convention to use.
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* What exception to raise on errors? ValueError, or a specialized exception?
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* Should you know what type you're expecting, or should the parsing figure
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it out? (e.g. ``parse_iso8601("yyyy-mm-dd")`` returns a ``date`` instance,
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but parsing "yyyy-mm-ddThh:mm:ss" returns a ``datetime``.) Should
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there be an option to signal an error if a time is provided where
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none is expected, or if no time is provided?
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* Anything special required for I18N? For time zones?
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Generic Input Parsing
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=======================
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Is a strptime() implementation that returns ``datetime`` types sufficient?
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XXX if yes, describe strptime here. Can the existing pure-Python
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implementation be easily retargeted?
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Output Formats
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=======================
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Not all input formats need to be supported as output formats, because it's
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pretty trivial to get the ``strftime()`` argument right for simple things
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such as YYYY/MM/DD. Only complicated formats need to be supported; :rfc:`2822`
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is currently the only one I can think of.
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Options:
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1) Provide predefined format strings, so you could write this::
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import datetime
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d = datetime.datetime(...)
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print d.strftime(d.RFC2822_FORMAT) # or datetime.RFC2822_FORMAT?
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2) Provide new methods on all the objects::
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d = datetime.datetime(...)
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print d.rfc822_time()
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Relevant functionality in other languages includes the `PHP date`_
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function (Python implementation by Simon Willison at
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http://simon.incutio.com/archive/2003/10/07/dateInPython)
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References
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==========
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.. _ISO8601: http://www.cl.cam.ac.uk/~mgk25/iso-time.html
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.. _ParseDate.pm: http://search.cpan.org/author/MUIR/Time-modules-2003.0211/lib/Time/ParseDate.pm
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.. _ctime: http://www.opengroup.org/onlinepubs/007908799/xsh/asctime.html
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.. _PHP date: http://www.php.net/date
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Other useful links:
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http://www.egenix.com/files/python/mxDateTime.html
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http://ringmaster.arc.nasa.gov/tools/time_formats.html
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http://www.thinkage.ca/english/gcos/expl/b/lib/0tosec.html
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https://moin.conectiva.com.br/DateUtil
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Copyright
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=========
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This document has been placed in the public domain.
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..
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End:
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