[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Change by Serhiy Storchaka :


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[issue28253] calendar.prcal(9999) output has a problem

[Donald Stufft]

Changes by Donald Stufft :


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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Changes by Alexander Belopolsky :


--
resolution:  -> fixed
stage: commit review -> resolved
status: open -> closed
superseder:  -> Make Calendar.itermonthdates() behave consistently in edge cases

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[issue28253] calendar.prcal(9999) output has a problem

[Roundup Robot]

Roundup Robot added the comment:

New changeset f2aff898f7c8 by Alexander Belopolsky in branch '2.7':
Issue #28253: Fixed calendar functions for extreme months: 0001-01 and -12.
https://hg.python.org/cpython/rev/f2aff898f7c8

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[issue28253] calendar.prcal(9999) output has a problem

[Roundup Robot]

Roundup Robot added the comment:

New changeset 7efba48299e9 by Alexander Belopolsky in branch 'default':
Issue #28253: Added a NEWS entry.
https://hg.python.org/cpython/rev/7efba48299e9

New changeset 55f11196c949 by Alexander Belopolsky in branch '3.5':
Issue #28253: Added a NEWS entry.
https://hg.python.org/cpython/rev/55f11196c949

New changeset 1f1a085f533f by Alexander Belopolsky in branch '3.6':
Issue #28253: Added a NEWS entry.
https://hg.python.org/cpython/rev/1f1a085f533f

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[issue28253] calendar.prcal(9999) output has a problem

[Roundup Robot]

Roundup Robot added the comment:

New changeset c439bce36bf2 by Alexander Belopolsky in branch '3.5':
Issue #28253: Fixed calendar functions for extreme months: 0001-01 and -12.
https://hg.python.org/cpython/rev/c439bce36bf2

New changeset cd384c4b441a by Alexander Belopolsky in branch '3.6':
Issue #28253: Fixed calendar functions for extreme months: 0001-01 and -12.
https://hg.python.org/cpython/rev/cd384c4b441a

New changeset bc285a9ecc58 by Alexander Belopolsky in branch 'default':
Issue #28253: Fixed calendar functions for extreme months: 0001-01 and -12.
https://hg.python.org/cpython/rev/bc285a9ecc58

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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assignee: serhiy.storchaka -> belopolsky

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

The patch LGTM.

You can see how itermonthdates() is used in third-party code:

https://github.com/sunlightlabs/django-locksmith/blob/master/locksmith/hub/dataviews.py
https://github.com/quandyfactory/Quandy/blob/master/quandy.py
https://github.com/takanory/plone.app.event/blob/master/plone/app/event/portlets/portlet_calendar.py
https://github.com/gerow/gnome-shell-google-calendar/blob/master/gnome-shell-google-calendar.py
https://bitbucket.org/benallard/msgboard/src/1c08fa3ba040f8151d0e28130b01b30e0595e448/msgboard/controller.py?at=default

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

issue28253-4.diff should be good now.

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Changes by Alexander Belopolsky :


Removed file: http://bugs.python.org/file44837/issue28253-4.diff

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Changes by Alexander Belopolsky :


Added file: http://bugs.python.org/file44845/issue28253-4.diff

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

Something went wrong with issue28253-4.diff.  I'll investigate and replace.

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

> The patch LGTM except tests.

What are your issues with the tests?  Did you see the -4 patch?

> But we should at least document the behavior of itermonthdates(), 
> monthdatescalendar() and yeardatescalendar() at corner cases.

I would rather not. At least not before we make under and overflow behavior 
consistent.  Frankly, I don't see why anyone would want to use these iterators.

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

The patch LGTM except tests.

But we should at least document the behavior of itermonthdates(), 
monthdatescalendar() and yeardatescalendar() at corner cases.

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[issue28253] calendar.prcal(9999) output has a problem

[Xiang Zhang]

Xiang Zhang added the comment:

Patch LGTM. 

> I would rather not mess up with itermonthdates(), particularly in a bugfix 
> release.  We can postpone the discussion of a better way to handle date 
> over/underflow in itermonthdates() until 3.7.

Before finally find a better way, can we at least make the two extreme cases 
behaviours consistent? Both emitting an exception or a shorter list.

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

issue28253-4.diff is issue28253-3.diff with tests.

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Added file: http://bugs.python.org/file44837/issue28253-4.diff

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

issue28253-3.diff uses itertools.repeat().

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Added file: http://bugs.python.org/file44836/issue28253-3.diff

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

issue28253-2.diff is a small performance improvement over issue28253.diff

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Added file: http://bugs.python.org/file44835/issue28253-2.diff

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

> unless we remove all date limits that is much harder issue

I don't think this is too hard.  I think the original implementation did not 
have date limits.  I've opened a separate issue for this.  See #28281.

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

I am attaching the proposed reimplementation of itermonthdays2() and 
itermonthdays().  It does not use itermonthdates() and is not that complicated. 
 It passes test_calendar, but I did not test it further than that.

I would rather not mess up with itermonthdates(), particularly in a bugfix 
release.  We can postpone the discussion of a better way to handle date 
over/underflow in itermonthdates() until 3.7.

--
Added file: http://bugs.python.org/file44834/issue28253.diff

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Yes, the current documentation is an impossibility (unless we remove all date 
limits that is much harder issue). Raisin OverflowError will make the 
implementation of itermonthdays2() and itermonthdays() more complex. Yielding 
dummy instances or None requires rewriting user code (less with a dummy 
instance if we are lucky). I agree that in long perspective yielding None looks 
better.

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

> itermonthdates() is documented public method

The current documentation is an impossibility:

"The iterator will yield datetime.date values and will always iterate through 
complete weeks, so it will yield dates outside the specified
month."

The current implementation deals with this impossibility differently for months 
(, 12) and (1, 1).  In the first case, the iterators stops on an out of 
bounds date:

>>> list(calendar.Calendar().itermonthdates(, 12))[-1]
datetime.date(, 12, 31)
>>> list(calendar.Calendar().itermonthdates(, 12))[-1].weekday()
4

but in the second, it raises the OverflowError:

>>> next(calendar.Calendar(1).itermonthdates(1, 1))
Traceback (most recent call last):
  File "", line 1, in 
  File "calendar.py", line 160, in itermonthdates
date -= datetime.timedelta(days=days)
OverflowError: date value out of range

Returning dummy instances instead of datetime.date in these cases will only 
make debugging harder for the users of .itermonthdates().  Sooner or later they 
would want to do something the returned value that the dummy won't support.  If 
you are willing to sacrifice the "will yield datetime.date values" for "will 
always iterate through complete weeks", I would make it yield None for out of 
bounds values and require the caller to deal with this possibility right away.

A better solution would be to simply raise OverflowError whenever the range of 
itermonthdates() does not fit within [date.min, date.max].

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

Note that the stop on date.max behavior was introduced in #15421.

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

itermonthdates() is documented public method. We should do something with it. 
Maybe emitting dummy data instances is the simplest way to solve this issue.

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

On the second thought, I don't see why itermonthdays2() and itermonthdays() 
need to use itermonthdates() at all.  It looks like it is easy to implement 
those using monthrange() and some simple integer arithmetics.

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[issue28253] calendar.prcal(9999) output has a problem

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

I would leave itermonthdates() alone and just fix itermonthdays2() (and 
itermonthdays() for consistency) as Xiang suggested.  The fix can be 
implemented by breaking on date.month != month and adding something like

for wd in range(date.weekday(), 7):
yield (0, wd)

after the existing for loop.

--
nosy: +belopolsky

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

The problem with year 1 was reported in issue26650.

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Having additional tests is always nice. After writing tests we can search 
whether there is other solution.

AFAIK the dummy data needs also the day attribute.

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[issue28253] calendar.prcal(9999) output has a problem

[Xiang Zhang]

Xiang Zhang added the comment:

How about the approach in calendar_prcal__demo.patch? If it's not bad I can 
add tests then.

--
Added file: http://bugs.python.org/file44793/calendar_prcal__demo.patch

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

This is not just not elegant, but it doesn't work if firstweekday is not 0.

The lowest level in the calendar module is itermonthdates(). But the problem is 
that dates outside supported range can't be represented.

While the output for December of the year  looks badly formatted, calendar 
doesn't work at all with January of the year 1 if firstweekday is not 0:

>>> import calendar
>>> calendar.setfirstweekday(6)
>>> calendar.prmonth(1, 1)
Traceback (most recent call last):
  File "", line 1, in 
  File "/home/serhiy/py/cpython-3.6/Lib/calendar.py", line 318, in prmonth
print(self.formatmonth(theyear, themonth, w, l), end=' ')
  File "/home/serhiy/py/cpython-3.6/Lib/calendar.py", line 331, in formatmonth
for week in self.monthdays2calendar(theyear, themonth):
  File "/home/serhiy/py/cpython-3.6/Lib/calendar.py", line 211, in 
monthdays2calendar
days = list(self.itermonthdays2(year, month))
  File "/home/serhiy/py/cpython-3.6/Lib/calendar.py", line 179, in 
itermonthdays2
for date in self.itermonthdates(year, month):
  File "/home/serhiy/py/cpython-3.6/Lib/calendar.py", line 162, in 
itermonthdates
date -= datetime.timedelta(days=days)
OverflowError: date value out of range

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[issue28253] calendar.prcal(9999) output has a problem

[Xiang Zhang]

Xiang Zhang added the comment:

Something like this?

diff -r 15f82b64eee0 Lib/calendar.py
--- a/Lib/calendar.py   Thu Sep 22 17:11:53 2016 -0700
+++ b/Lib/calendar.py   Fri Sep 23 16:27:03 2016 +0800
@@ -181,6 +181,9 @@
 yield (0, date.weekday())
 else:
 yield (date.day, date.weekday())
+if year ==  and month == 12 and date.day == 31:
+yield (0, 6)
+yield (0, 7)
 
 def itermonthdays(self, year, month):
 """

Is there a more elegant way? I considered this but didn't quite like it so 
abandoned it.

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Html calendar formats the last week differently for years 9982 and .

Year 9982:
2728293031

Year :
2728293031

I think this issue should be fixed on lower level than text calendar formatter.

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[issue28253] calendar.prcal(9999) output has a problem

[Xiang Zhang]

Changes by Xiang Zhang :


--
keywords: +patch
Added file: http://bugs.python.org/file44789/calendar_pryear_.patch

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[issue28253] calendar.prcal(9999) output has a problem

[Xiang Zhang]

Xiang Zhang added the comment:

calendar internally relies on datetime and uses datetime.date. datetime.date 
can't represent date more than .12.31 so some logic is broken for 
it(normally the week list should be of length 7, date outside the month will be 
(0, x) pair but this is not the case for .12). This won't affect prmonth 
since it doesn't do center formatting. We can change to that behaviour to fix 
this. calendar_pryear_ tires to fix this.

--
nosy: +xiang.zhang

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[issue28253] calendar.prcal(9999) output has a problem

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Thank you for your report lijp. This is interesting issue. It is not specific 
for Windows.

itermonthdates() yields shortened sequence of dates at the end of maximal year. 
The formatted row of day numbers is centered. Since the number of days is less 
than expected, additional spaces are added at the left.

--
assignee:  -> serhiy.storchaka
components: +Library (Lib) -Windows
nosy: +rhettinger, serhiy.storchaka -paul.moore, steve.dower, tim.golden, 
zach.ware
versions: +Python 2.7, Python 3.5, Python 3.6, Python 3.7 -Python 3.4

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[issue28253] calendar.prcal(9999) output has a problem

[lijp]

Changes by lijp :


Added file: http://bugs.python.org/file44788/20160923154147.png

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[issue28253] calendar.prcal(9999) output has a problem

[lijp]

Changes by lijp :


--
components: +Windows
nosy: +paul.moore, steve.dower, tim.golden, zach.ware
title: the reply's additional "Re:" -> calendar.prcal() output has a problem
type:  -> behavior
versions: +Python 3.4

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