Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
MRAB wrote: And when someone says January 30, do they really mean the day before the last day of the month? No, no, that's January -2, a *completely* different thing! -- Greg -- http://mail.python.org/mailman/listinfo/python-list
Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
greg g...@cosc.canterbury.ac.nz (g) wrote: g MRAB wrote: And when someone says January 30, do they really mean the day before the last day of the month? g No, no, that's January -2, a *completely* different thing! But for someone else it would be February -2. -- Piet van Oostrum p...@vanoostrum.org WWW: http://pietvanoostrum.com/ PGP key: [8DAE142BE17999C4] -- http://mail.python.org/mailman/listinfo/python-list
Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
On Mon, Oct 12, 2009 at 4:27 AM, Piet van Oostrum p...@cs.uu.nl wrote: greg g...@cosc.canterbury.ac.nz (g) wrote: g MRAB wrote: And when someone says January 30, do they really mean the day before the last day of the month? g No, no, that's January -2, a *completely* different thing! But for someone else it would be February -2. And for still others, it's the last $DAYOFWEEK of the month, which just happened to fall on the 30th. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
Piet van Oostrum wrote: greg g...@cosc.canterbury.ac.nz (g) wrote: g MRAB wrote: And when someone says January 30, do they really mean the day before the last day of the month? g No, no, that's January -2, a *completely* different thing! But for someone else it would be February -2. When is February 0? :-) -- http://mail.python.org/mailman/listinfo/python-list
Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
Tim Chase wrote: Month arithmetic is a bit of a mess, since it's not clear how to map e.g. Jan 31 + one month. Jan 31 + one month usually means add one to the month value and then keep backing off the day if you get an exception making the date, so you'd get Feb 31, exception, Feb 30, exception, Feb 29, possibly an exception, and possibly/finally Feb 28th. This makes pretty intuitive sense to most folks and is usually what's meant. Well, yes, but that's just one way to solve the problem. I guess I'll just add all possible solutions and then let the user decide what's best in some way. I've found that issues and confusion stem more from the non-commutative reality that Jan 31 + (1 month) + (-1 month) != Jan 31 + (-1 month) + (1 month) or the non-associative Jan 31 + (1 month + 1 month) != (Jan 31 + 1 month) + 1 month :-/ That's why mxDateTime actually returning a day in March... mx.DateTime.DateTime(2009, 1, 31) + mx.DateTime.RelativeDateTime(months=+1) mx.DateTime.DateTime object for '2009-03-03 00:00:00.00' at 2ba43f93ebe0 That's intuitive for mathematicians only, though ;-) So yes, messy it is! Indeed. -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Oct 12 2009) Python/Zope Consulting and Support ...http://www.egenix.com/ mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/ mxODBC, mxDateTime, mxTextTools ...http://python.egenix.com/ ::: Try our new mxODBC.Connect Python Database Interface for free ! eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ -- http://mail.python.org/mailman/listinfo/python-list
Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
Rhodri James wrote: On Fri, 09 Oct 2009 13:39:43 +0100, Tim Chase python.l...@tim.thechases.com wrote: Month arithmetic is a bit of a mess, since it's not clear how to map e.g. Jan 31 + one month. Jan 31 + one month usually means add one to the month value and then keep backing off the day if you get an exception making the date, so you'd get Feb 31, exception, Feb 30, exception, Feb 29, possibly an exception, and possibly/finally Feb 28th. This makes pretty intuitive sense to most folks and is usually what's meant. I've found that issues and confusion stem more from the non-commutative reality that Jan 31 + (1 month) + (-1 month) != Jan 31 + (-1 month) + (1 month) or the non-associative Jan 31 + (1 month + 1 month) != (Jan 31 + 1 month) + 1 month :-/ I'd hazard a guess that what we're actually seeing is people mentally rebasing their indices, i.e. counting from the end of the month rather than the start, which makes the last day of January and January 31 not the same thing really. Unfortunately we're very fuzzy about when we do things like this, which makes it hard on a poor programmer. Ah, for that we have RelativeDateTime: # next month, last day of the month mx.DateTime.DateTime(2009, 1, 31) + mx.DateTime.RelativeDateTime(months=+1, day=-1) mx.DateTime.DateTime object for '2009-02-28 00:00:00.00' at 2ba43f95c088 -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Oct 12 2009) Python/Zope Consulting and Support ...http://www.egenix.com/ mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/ mxODBC, mxDateTime, mxTextTools ...http://python.egenix.com/ ::: Try our new mxODBC.Connect Python Database Interface for free ! eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ -- http://mail.python.org/mailman/listinfo/python-list
Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
Chris Rebert wrote: On Mon, Oct 12, 2009 at 4:27 AM, Piet van Oostrum p...@cs.uu.nl wrote: greg g...@cosc.canterbury.ac.nz (g) wrote: g MRAB wrote: And when someone says January 30, do they really mean the day before the last day of the month? g No, no, that's January -2, a *completely* different thing! But for someone else it would be February -2. And for still others, it's the last $DAYOFWEEK of the month, which just happened to fall on the 30th. That's a little more complicated: mx.DateTime.DateTime(2009, 1, 31).day_of_week 5 # which is a ... mx.DateTime.Weekday[mx.DateTime.DateTime(2009, 1, 31).day_of_week] 'Saturday' Now: # next month, last Saturday mx.DateTime.DateTime(2009, 1, 31) + mx.DateTime.RelativeDateTime(months=+1, day=1, weekday=(5, -1)) mx.DateTime.DateTime object for '2009-02-28 00:00:00.00' at 2ba43f93ebe0 -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Oct 12 2009) Python/Zope Consulting and Support ...http://www.egenix.com/ mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/ mxODBC, mxDateTime, mxTextTools ...http://python.egenix.com/ ::: Try our new mxODBC.Connect Python Database Interface for free ! eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ -- http://mail.python.org/mailman/listinfo/python-list
Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
On Fri, 09 Oct 2009 13:39:43 +0100, Tim Chase python.l...@tim.thechases.com wrote: Month arithmetic is a bit of a mess, since it's not clear how to map e.g. Jan 31 + one month. Jan 31 + one month usually means add one to the month value and then keep backing off the day if you get an exception making the date, so you'd get Feb 31, exception, Feb 30, exception, Feb 29, possibly an exception, and possibly/finally Feb 28th. This makes pretty intuitive sense to most folks and is usually what's meant. I've found that issues and confusion stem more from the non-commutative reality that Jan 31 + (1 month) + (-1 month) != Jan 31 + (-1 month) + (1 month) or the non-associative Jan 31 + (1 month + 1 month) != (Jan 31 + 1 month) + 1 month :-/ I'd hazard a guess that what we're actually seeing is people mentally rebasing their indices, i.e. counting from the end of the month rather than the start, which makes the last day of January and January 31 not the same thing really. Unfortunately we're very fuzzy about when we do things like this, which makes it hard on a poor programmer. -- Rhodri James *-* Wildebeest Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
Rhodri James wrote: On Fri, 09 Oct 2009 13:39:43 +0100, Tim Chase python.l...@tim.thechases.com wrote: Month arithmetic is a bit of a mess, since it's not clear how to map e.g. Jan 31 + one month. Jan 31 + one month usually means add one to the month value and then keep backing off the day if you get an exception making the date, so you'd get Feb 31, exception, Feb 30, exception, Feb 29, possibly an exception, and possibly/finally Feb 28th. This makes pretty intuitive sense to most folks and is usually what's meant. I've found that issues and confusion stem more from the non-commutative reality that Jan 31 + (1 month) + (-1 month) != Jan 31 + (-1 month) + (1 month) or the non-associative Jan 31 + (1 month + 1 month) != (Jan 31 + 1 month) + 1 month :-/ I'd hazard a guess that what we're actually seeing is people mentally rebasing their indices, i.e. counting from the end of the month rather than the start, which makes the last day of January and January 31 not the same thing really. Unfortunately we're very fuzzy about when we do things like this, which makes it hard on a poor programmer. And when someone says January 30, do they really mean the day before the last day of the month? Where would it end? :-) -- http://mail.python.org/mailman/listinfo/python-list
Re: mxDateTime history (Re: mktime, how to handle dates before 01-01-1970 ?)
Month arithmetic is a bit of a mess, since it's not clear how to map e.g. Jan 31 + one month. Jan 31 + one month usually means add one to the month value and then keep backing off the day if you get an exception making the date, so you'd get Feb 31, exception, Feb 30, exception, Feb 29, possibly an exception, and possibly/finally Feb 28th. This makes pretty intuitive sense to most folks and is usually what's meant. I've found that issues and confusion stem more from the non-commutative reality that Jan 31 + (1 month) + (-1 month) != Jan 31 + (-1 month) + (1 month) or the non-associative Jan 31 + (1 month + 1 month) != (Jan 31 + 1 month) + 1 month :-/ So yes, messy it is! -tkc -- http://mail.python.org/mailman/listinfo/python-list
