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bpo-36004: Add date.fromisocalendar (GH-11888) 

This commit implements the first version of date.fromisocalendar, the
inverse function for date.isocalendar.
This commit is contained in:
Paul Ganssle 2019-04-29 09:22:03 -04:00 committed by Victor Stinner
parent a86e06433a
commit 88c0937056
6 changed files with 209 additions and 0 deletions
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17
Doc/library/datetime.rst
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@ -458,6 +458,13 @@ Other constructors, all class methods:
.. versionadded:: 3.7
.. classmethod:: date.fromisocalendar(year, week, day)
Return a :class:`date` corresponding to the ISO calendar date specified by
year, week and day. This is the inverse of the function :meth:`date.isocalendar`.
.. versionadded:: 3.8
Class attributes:
@ -854,6 +861,16 @@ Other constructors, all class methods:
.. versionadded:: 3.7
.. classmethod:: datetime.fromisocalendar(year, week, day)
Return a :class:`datetime` corresponding to the ISO calendar date specified
by year, week and day. The non-date components of the datetime are populated
with their normal default values. This is the inverse of the function
:meth:`datetime.isocalendar`.
.. versionadded:: 3.8
.. classmethod:: datetime.strptime(date_string, format)
Return a :class:`.datetime` corresponding to *date_string*, parsed according to

10
Doc/whatsnew/3.8.rst
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@ -244,6 +244,16 @@ where the DLL is stored (if a full or partial path is used to load the initial
DLL) and paths added by :func:`~os.add_dll_directory`.
datetime
--------
Added new alternate constructors :meth:`datetime.date.fromisocalendar` and
:meth:`datetime.datetime.fromisocalendar`, which construct :class:`date` and
:class:`datetime` objects respectively from ISO year, week number and weekday;
these are the inverse of each class's ``isocalendar`` method.
(Contributed by Paul Ganssle in :issue:`36004`.)
gettext
-------

35
Lib/datetime.py
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@ -884,6 +884,40 @@ class date:
except Exception:
raise ValueError(f'Invalid isoformat string: {date_string!r}')
@classmethod
def fromisocalendar(cls, year, week, day):
"""Construct a date from the ISO year, week number and weekday.
This is the inverse of the date.isocalendar() function"""
# Year is bounded this way because 9999-12-31 is (9999, 52, 5)
if not MINYEAR <= year <= MAXYEAR:
raise ValueError(f"Year is out of range: {year}")
if not 0 < week < 53:
out_of_range = True
if week == 53:
# ISO years have 53 weeks in them on years starting with a
# Thursday and leap years starting on a Wednesday
first_weekday = _ymd2ord(year, 1, 1) % 7
if (first_weekday == 4 or (first_weekday == 3 and
_is_leap(year))):
out_of_range = False
if out_of_range:
raise ValueError(f"Invalid week: {week}")
if not 0 < day < 8:
raise ValueError(f"Invalid weekday: {day} (range is [1, 7])")
# Now compute the offset from (Y, 1, 1) in days:
day_offset = (week - 1) * 7 + (day - 1)
# Calculate the ordinal day for monday, week 1
day_1 = _isoweek1monday(year)
ord_day = day_1 + day_offset
return cls(*_ord2ymd(ord_day))
# Conversions to string
@ -2141,6 +2175,7 @@ def _isoweek1monday(year):
week1monday += 7
return week1monday
class timezone(tzinfo):
__slots__ = '_offset', '_name'

76
Lib/test/datetimetester.py
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@ -1795,6 +1795,82 @@ class TestDate(HarmlessMixedComparison, unittest.TestCase):
with self.assertRaises(TypeError):
self.theclass.fromisoformat(bad_type)
def test_fromisocalendar(self):
# For each test case, assert that fromisocalendar is the
# inverse of the isocalendar function
dates = [
(2016, 4, 3),
(2005, 1, 2), # (2004, 53, 7)
(2008, 12, 30), # (2009, 1, 2)
(2010, 1, 2), # (2009, 53, 6)
(2009, 12, 31), # (2009, 53, 4)
(1900, 1, 1), # Unusual non-leap year (year % 100 == 0)
(1900, 12, 31),
(2000, 1, 1), # Unusual leap year (year % 400 == 0)
(2000, 12, 31),
(2004, 1, 1), # Leap year
(2004, 12, 31),
(1, 1, 1),
(9999, 12, 31),
(MINYEAR, 1, 1),
(MAXYEAR, 12, 31),
]
for datecomps in dates:
with self.subTest(datecomps=datecomps):
dobj = self.theclass(*datecomps)
isocal = dobj.isocalendar()
d_roundtrip = self.theclass.fromisocalendar(*isocal)
self.assertEqual(dobj, d_roundtrip)
def test_fromisocalendar_value_errors(self):
isocals = [
(2019, 0, 1),
(2019, -1, 1),
(2019, 54, 1),
(2019, 1, 0),
(2019, 1, -1),
(2019, 1, 8),
(2019, 53, 1),
(10000, 1, 1),
(0, 1, 1),
(9999999, 1, 1),
(2<<32, 1, 1),
(2019, 2<<32, 1),
(2019, 1, 2<<32),
]
for isocal in isocals:
with self.subTest(isocal=isocal):
with self.assertRaises(ValueError):
self.theclass.fromisocalendar(*isocal)
def test_fromisocalendar_type_errors(self):
err_txformers = [
str,
float,
lambda x: None,
]
# Take a valid base tuple and transform it to contain one argument
# with the wrong type. Repeat this for each argument, e.g.
# [("2019", 1, 1), (2019, "1", 1), (2019, 1, "1"), ...]
isocals = []
base = (2019, 1, 1)
for i in range(3):
for txformer in err_txformers:
err_val = list(base)
err_val[i] = txformer(err_val[i])
isocals.append(tuple(err_val))
for isocal in isocals:
with self.subTest(isocal=isocal):
with self.assertRaises(TypeError):
self.theclass.fromisocalendar(*isocal)
#############################################################################
# datetime tests

4
Misc/NEWS.d/next/Library/2019-02-17-12-55-51.bpo-36004.hCt_KK.rst Normal file
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@ -0,0 +1,4 @@
Added new alternate constructors :meth:`datetime.date.fromisocalendar` and
:meth:`datetime.datetime.fromisocalendar`, which construct date objects from
ISO year, week number and weekday; these are the inverse of each class's
``isocalendar`` method. Patch by Paul Ganssle.

67
Modules/_datetimemodule.c
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@ -3003,6 +3003,67 @@ invalid_string_error:
return NULL;
}
static PyObject *
date_fromisocalendar(PyObject *cls, PyObject *args, PyObject *kw)
{
static char *keywords[] = {
"year", "week", "day", NULL
};
int year, week, day;
if (PyArg_ParseTupleAndKeywords(args, kw, "iii:fromisocalendar",
keywords,
&year, &week, &day) == 0) {
if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
PyErr_Format(PyExc_ValueError,
"ISO calendar component out of range");
}
return NULL;
}
// Year is bounded to 0 < year < 10000 because 9999-12-31 is (9999, 52, 5)
if (year < MINYEAR || year > MAXYEAR) {
PyErr_Format(PyExc_ValueError, "Year is out of range: %d", year);
return NULL;
}
if (week <= 0 || week >= 53) {
int out_of_range = 1;
if (week == 53) {
// ISO years have 53 weeks in it on years starting with a Thursday
// and on leap years starting on Wednesday
int first_weekday = weekday(year, 1, 1);
if (first_weekday == 3 || (first_weekday == 2 && is_leap(year))) {
out_of_range = 0;
}
}
if (out_of_range) {
PyErr_Format(PyExc_ValueError, "Invalid week: %d", week);
return NULL;
}
}
if (day <= 0 || day >= 8) {
PyErr_Format(PyExc_ValueError, "Invalid day: %d (range is [1, 7])",
day);
return NULL;
}
// Convert (Y, W, D) to (Y, M, D) in-place
int day_1 = iso_week1_monday(year);
int month = week;
int day_offset = (month - 1)*7 + day - 1;
ord_to_ymd(day_1 + day_offset, &year, &month, &day);
return new_date_subclass_ex(year, month, day, cls);
}
/*
* Date arithmetic.
*/
@ -3296,6 +3357,12 @@ static PyMethodDef date_methods[] = {
METH_CLASS,
PyDoc_STR("str -> Construct a date from the output of date.isoformat()")},
{"fromisocalendar", (PyCFunction)(void(*)(void))date_fromisocalendar,
METH_VARARGS | METH_KEYWORDS | METH_CLASS,
PyDoc_STR("int, int, int -> Construct a date from the ISO year, week "
"number and weekday.\n\n"
"This is the inverse of the date.isocalendar() function")},
{"today", (PyCFunction)date_today, METH_NOARGS | METH_CLASS,
PyDoc_STR("Current date or datetime: same as "
"self.__class__.fromtimestamp(time.time()).")},