PEP 321: Date/Time Parsing and Formatting

[Paddy McCarthy]

Gerrit Holl wrote:
> Posted with permission from the author.
> I have some comments on this PEP, see the (coming) followup to this message.
> 
> PEP: 321
> Title: Date/Time Parsing and Formatting
<<SNIP>>
> 
> Abstract
> ========
> 
> 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.
> 
<<SNIP>>
>    	
> 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 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?
> 

I am in favour of there being an intelligent  'guess the format'
routine  that would be easy to use, but maybe computationally
inefficient, backed up by a computationally efficient routine where
you specify the format. This latter case being split into two sub
items: first where the parsing routine is passed a constant
representing one of the standard formats and another where the parsing
routine is passed a string representing the format.
  datetime.datetime.parse("

 datetime.datetime.parse("1985-08-13 15:03")
 gives: datetime(1985, 8, 13, 13, 5)
 datetime.date.parse("1985-08-13 15:03")
 gives: date(1985, 8, 13) # You asked for the date, date was found 
                          # first in string and converted
 datetime.date.parse("13/08/1985", "%d/%m/%Y")
 gives: date(1985, 8, 13)
 datetime.datetime.parse("1985-08-13 15:03", datetime.ISO8601)
 gives: datetime(1985, 8, 13, 13, 5)

The idea being for the parser to be able to automatically extract a
date from one of the standard formats it knows, or to accept a
strptime type string for unknown formats.

(Apologies to Gerrit for using values from his reply)

Cheers, Paddy.