calendar: OverflowErrors for year == 1 and firstweekday > 0

[mjpieters]

BPO	26650
Nosy	@rhettinger, @mjpieters, @abalkin
Superseder	bpo-28292: Make Calendar.itermonthdates() behave consistently in edge cases
Files	issue26650.diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/abalkin'
closed_at = <Date 2016-09-28.03:04:31.303>
created_at = <Date 2016-03-27.09:38:56.897>
labels = ['type-bug', 'library']
title = 'calendar: OverflowErrors for year == 1 and firstweekday > 0'
updated_at = <Date 2016-09-28.03:04:31.302>
user = 'https://github.com/mjpieters'

bugs.python.org fields:

activity = <Date 2016-09-28.03:04:31.302>
actor = 'belopolsky'
assignee = 'belopolsky'
closed = True
closed_date = <Date 2016-09-28.03:04:31.303>
closer = 'belopolsky'
components = ['Library (Lib)']
creation = <Date 2016-03-27.09:38:56.897>
creator = 'mjpieters'
dependencies = []
files = ['42305']
hgrepos = []
issue_num = 26650
keywords = ['patch']
message_count = 3.0
messages = ['262514', '262515', '277477']
nosy_count = 4.0
nosy_names = ['rhettinger', 'mjpieters', 'belopolsky', 'SilentGhost']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '28292'
type = 'behavior'
url = 'https://bugs.python.org/issue26650'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6']

[mjpieters]

For anything other than calendar.Calendar(0), many methods lead to OverflowError exceptions:

>>> import calendar
>>> c = calendar.Calendar(0)
>>> list(c.itermonthdays(1, 1))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 0, 0, 0, 0]
>>> c = calendar.Calendar(1)
>>> list(c.itermonthdays(1, 1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python2.7/calendar.py", line 188, in itermonthdays
    for date in self.itermonthdates(year, month):
  File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python2.7/calendar.py", line 160, in itermonthdates
    date -= datetime.timedelta(days=days)
OverflowError: date value out of range

This echoes a similar problem with year = 9999, see issue bpo-15421

[SilentGhost]

Here is the patch. Both this patch and the fix for bpo-15421 might violate the documented behaviour of getting the full week's worth of dates. I wonder if that should also be documented.

[abalkin]

My patch for bpo-28253 fixes this problem for itermonthdays2() and itermonthdays() methods. As discussed there, fixing itermonthdates() would require changing a documented public interface.