[Python-Dev] dateutil

[Robert Brewer]

Skip Montanaro wrote:
> I'd like to try out your natural language parser, but can't 
> find it.  I
> naively thought this might work, but it doesn't:
> 
>     >>> import recur
>     >>> import datetime
>     >>> for eachDate in recur.Recurrence(datetime.date(2004, 
> 1, 7), "every 4 days", datetime.date(2004, 4, 15)):
>     ...   print eachDate
>     ... 
>     Traceback (most recent call last):
>       File "<stdin>", line 1, in ?
>       File "recur.py", line 599, in __init__
>         raise ValueError, (u"The supplied description ('%s') "
>     ValueError: The supplied description ('every 4 days') 
> could not be parsed.

In this case, use:
>>> import recur
>>> import datetime
>>> for eachDate in recur.Recurrence(datetime.date(2004, 1, 7), "4
days", datetime.date(2004, 4, 15)):
... 	print eachDate
... 	
2004-01-07
2004-01-11
2004-01-15
2004-01-19
2004-01-23
2004-01-27
2004-01-31
2004-02-04
2004-02-08
2004-02-12
2004-02-16
2004-02-20
2004-02-24
2004-02-28
2004-03-03
2004-03-07
2004-03-11
2004-03-15
2004-03-19
2004-03-23
2004-03-27
2004-03-31
2004-04-04
2004-04-08
2004-04-12

It would be a simple thing to fix by changing a regex in
Locale.patterns[byunits] from r"([0-9]+) days?" to r"(?:every )?([0-9]+)
days?"  I'll probably add this to my default Locale class, but one of
the reasons I made a separate Locale class in the first place was to
facilitate such modification via subclassing.

> I realize this is a usage question and python-dev isn't a usage list.
> Still, it suggests that perhaps the community as a whole 
> needs a bit more
> exposure to these concepts before they are incorporated into 
> the standard
> library.  Perhaps a PEP about recurrence relations is warranted.

As Gustavo has pointed out, the internal, representational details have
been pretty much nailed in the iCal RFC. But I agree with you that
wrapping them for locale-specific, end-user ease-of-use is important. I
wouldn't worry about a PEP unless DateUtil approaches Library inclusion
status.


Robert Brewer
MIS
Amor Ministries
fumanchu at amor.org