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bpo-31222: Make (datetime|date|time).replace return subclass type in Pure Python #4176

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Merged
merged 3 commits into from
Nov 9, 2017
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bpo-31222: Make (datetime|date|time).replace return subclass type in Pure Python #4176

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511e2f1
Add failing test for pure Python datetime subclasses
pganssle Oct 30, 2017
dea1eaf
Bring pure Python (datetime|date|time).replace behavior in line with C
pganssle Oct 30, 2017
8f26dd3
Use more descriptive subclass names in subclass_replace
pganssle Nov 5, 2017
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6 changes: 3 additions & 3 deletions Lib/datetime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -828,7 +828,7 @@ def replace(self, year=None, month=None, day=None):
month = self._month
if day is None:
day = self._day
return date(year, month, day)
return type(self)(year, month, day)
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@vstinner vstinner Oct 30, 2017 •
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I prefer self.__class__, but I never know which one is the best :-)

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I don't have any real preference here. I usually go with self.__class__ myself, but I was somewhat persuaded by the discussion on StackOverflow that seemed to indicate that they are equivalent in Python 3, and that type is shorter - seemed like a mixed bag as to which one is more intuitive. I'm happy to change it to the "house style".

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Not sure if it's even a relevant precedent, since they're in two different languages, but it does seem that the C source code uses Py_TYPE(self) rather than some equivalent of self.__class__. Though for all I know that's a macro that expands to self.__class__...


# Comparisons of date objects with other.

Expand Down Expand Up @@ -1316,7 +1316,7 @@ def replace(self, hour=None, minute=None, second=None, microsecond=None,
tzinfo = self.tzinfo
if fold is None:
fold = self._fold
return time(hour, minute, second, microsecond, tzinfo, fold=fold)
return type(self)(hour, minute, second, microsecond, tzinfo, fold=fold)

# Pickle support.

Expand Down Expand Up @@ -1597,7 +1597,7 @@ def replace(self, year=None, month=None, day=None, hour=None,
tzinfo = self.tzinfo
if fold is None:
fold = self.fold
return datetime(year, month, day, hour, minute, second,
return type(self)(year, month, day, hour, minute, second,
microsecond, tzinfo, fold=fold)

def _local_timezone(self):
Expand Down
14 changes: 14 additions & 0 deletions Lib/test/datetimetester.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1520,6 +1520,13 @@ def test_replace(self):
base = cls(2000, 2, 29)
self.assertRaises(ValueError, base.replace, year=2001)

def test_subclass_replace(self):
class DateSubclass(self.theclass):
pass

dt = DateSubclass(2012, 1, 1)
self.assertIs(type(dt.replace(year=2013)), DateSubclass)

def test_subclass_date(self):

class C(self.theclass):
Expand Down Expand Up @@ -2626,6 +2633,13 @@ def test_replace(self):
self.assertRaises(ValueError, base.replace, second=100)
self.assertRaises(ValueError, base.replace, microsecond=1000000)

def test_subclass_replace(self):
class TimeSubclass(self.theclass):
pass

ctime = TimeSubclass(12, 30)
self.assertIs(type(ctime.replace(hour=10)), TimeSubclass)

def test_subclass_time(self):

class C(self.theclass):
Expand Down