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Implement weekday shifting for arrow-py#64
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I’m not terribly happy with the implementation - I don’t grok why
dateutil handles some values (negatives and zeroes) the way it does,
but I figure this is good to generate discussion anyway.
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@BonkaBonka
BonkaBonka committed Dec 7, 2016
1 parent 4996bc9 commit d949820
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17 changes: 16 additions & 1 deletion arrow/arrow.py
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Original file line number Diff line number Diff line change
Expand Up @@ -471,13 +471,28 @@ def shift(self, **kwargs):
>>> arw.shift(years=1, months=-1)
<Arrow [2014-04-11T22:27:34.787885+00:00]>
Day-of-the-week relative shifting can use either Python's weekday numbers
(Monday = 0, Tuesday = 1 .. Sunday = 6) or using dateutil.relativedelta's
day instances (MO, TU .. SU). When using weekday numbers, the returned
date will always be greater than or equal to the starting date.
Using the above code (which is a Saturday) and asking it to shift to Saturday:
>>> arw.shift(weekday=5)
<Arrow [2013-05-11T22:27:34.787885+00:00]>
While asking for a Monday:
>>> arw.shift(weekday=0)
<Arrow [2013-05-13T22:27:34.787885+00:00]>
'''

relative_kwargs = {}

for key, value in kwargs.items():

if key in self._ATTRS_PLURAL or key in ['weeks', 'quarters']:
if key in self._ATTRS_PLURAL or key in ['weeks', 'quarters', 'weekday']:
relative_kwargs[key] = value
else:
raise AttributeError()
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64 changes: 64 additions & 0 deletions tests/arrow_tests.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@

from datetime import date, datetime, timedelta
from dateutil import tz
from dateutil.relativedelta import MO, TU, WE, TH, FR, SA, SU
import simplejson as json
import warnings
import calendar
Expand Down Expand Up @@ -592,6 +593,48 @@ def test_shift(self):
assertEqual(arw.shift(seconds=1), arrow.Arrow(2013, 5, 5, 12, 30, 46))
assertEqual(arw.shift(microseconds=1), arrow.Arrow(2013, 5, 5, 12, 30, 45, 1))

# Remember: Python's weekday 0 is Monday
assertEqual(arw.shift(weekday=0), arrow.Arrow(2013, 5, 6, 12, 30, 45))
assertEqual(arw.shift(weekday=1), arrow.Arrow(2013, 5, 7, 12, 30, 45))
assertEqual(arw.shift(weekday=2), arrow.Arrow(2013, 5, 8, 12, 30, 45))
assertEqual(arw.shift(weekday=3), arrow.Arrow(2013, 5, 9, 12, 30, 45))
assertEqual(arw.shift(weekday=4), arrow.Arrow(2013, 5, 10, 12, 30, 45))
assertEqual(arw.shift(weekday=5), arrow.Arrow(2013, 5, 11, 12, 30, 45))
assertEqual(arw.shift(weekday=6), arw)

with assertRaises(IndexError):
arw.shift(weekday=7)

# Use dateutil.relativedelta's convenient day instances
assertEqual(arw.shift(weekday=MO), arrow.Arrow(2013, 5, 6, 12, 30, 45))
assertEqual(arw.shift(weekday=MO(0)), arrow.Arrow(2013, 5, 6, 12, 30, 45))
assertEqual(arw.shift(weekday=MO(1)), arrow.Arrow(2013, 5, 6, 12, 30, 45))
assertEqual(arw.shift(weekday=MO(2)), arrow.Arrow(2013, 5, 13, 12, 30, 45))
assertEqual(arw.shift(weekday=TU), arrow.Arrow(2013, 5, 7, 12, 30, 45))
assertEqual(arw.shift(weekday=TU(0)), arrow.Arrow(2013, 5, 7, 12, 30, 45))
assertEqual(arw.shift(weekday=TU(1)), arrow.Arrow(2013, 5, 7, 12, 30, 45))
assertEqual(arw.shift(weekday=TU(2)), arrow.Arrow(2013, 5, 14, 12, 30, 45))
assertEqual(arw.shift(weekday=WE), arrow.Arrow(2013, 5, 8, 12, 30, 45))
assertEqual(arw.shift(weekday=WE(0)), arrow.Arrow(2013, 5, 8, 12, 30, 45))
assertEqual(arw.shift(weekday=WE(1)), arrow.Arrow(2013, 5, 8, 12, 30, 45))
assertEqual(arw.shift(weekday=WE(2)), arrow.Arrow(2013, 5, 15, 12, 30, 45))
assertEqual(arw.shift(weekday=TH), arrow.Arrow(2013, 5, 9, 12, 30, 45))
assertEqual(arw.shift(weekday=TH(0)), arrow.Arrow(2013, 5, 9, 12, 30, 45))
assertEqual(arw.shift(weekday=TH(1)), arrow.Arrow(2013, 5, 9, 12, 30, 45))
assertEqual(arw.shift(weekday=TH(2)), arrow.Arrow(2013, 5, 16, 12, 30, 45))
assertEqual(arw.shift(weekday=FR), arrow.Arrow(2013, 5, 10, 12, 30, 45))
assertEqual(arw.shift(weekday=FR(0)), arrow.Arrow(2013, 5, 10, 12, 30, 45))
assertEqual(arw.shift(weekday=FR(1)), arrow.Arrow(2013, 5, 10, 12, 30, 45))
assertEqual(arw.shift(weekday=FR(2)), arrow.Arrow(2013, 5, 17, 12, 30, 45))
assertEqual(arw.shift(weekday=SA), arrow.Arrow(2013, 5, 11, 12, 30, 45))
assertEqual(arw.shift(weekday=SA(0)), arrow.Arrow(2013, 5, 11, 12, 30, 45))
assertEqual(arw.shift(weekday=SA(1)), arrow.Arrow(2013, 5, 11, 12, 30, 45))
assertEqual(arw.shift(weekday=SA(2)), arrow.Arrow(2013, 5, 18, 12, 30, 45))
assertEqual(arw.shift(weekday=SU), arw)
assertEqual(arw.shift(weekday=SU(0)), arw)
assertEqual(arw.shift(weekday=SU(1)), arw)
assertEqual(arw.shift(weekday=SU(2)), arrow.Arrow(2013, 5, 12, 12, 30, 45))

def test_shift_negative(self):

arw = arrow.Arrow(2013, 5, 5, 12, 30, 45)
Expand All @@ -607,6 +650,27 @@ def test_shift_negative(self):
assertEqual(arw.shift(seconds=-1), arrow.Arrow(2013, 5, 5, 12, 30, 44))
assertEqual(arw.shift(microseconds=-1), arrow.Arrow(2013, 5, 5, 12, 30, 44, 999999))

# Not sure how practical these negative weekdays are
assertEqual(arw.shift(weekday=-1), arw.shift(weekday=SU))
assertEqual(arw.shift(weekday=-2), arw.shift(weekday=SA))
assertEqual(arw.shift(weekday=-3), arw.shift(weekday=FR))
assertEqual(arw.shift(weekday=-4), arw.shift(weekday=TH))
assertEqual(arw.shift(weekday=-5), arw.shift(weekday=WE))
assertEqual(arw.shift(weekday=-6), arw.shift(weekday=TU))
assertEqual(arw.shift(weekday=-7), arw.shift(weekday=MO))

with assertRaises(IndexError):
arw.shift(weekday=-8)

assertEqual(arw.shift(weekday=MO(-1)), arrow.Arrow(2013, 4, 29, 12, 30, 45))
assertEqual(arw.shift(weekday=TU(-1)), arrow.Arrow(2013, 4, 30, 12, 30, 45))
assertEqual(arw.shift(weekday=WE(-1)), arrow.Arrow(2013, 5, 1, 12, 30, 45))
assertEqual(arw.shift(weekday=TH(-1)), arrow.Arrow(2013, 5, 2, 12, 30, 45))
assertEqual(arw.shift(weekday=FR(-1)), arrow.Arrow(2013, 5, 3, 12, 30, 45))
assertEqual(arw.shift(weekday=SA(-1)), arrow.Arrow(2013, 5, 4, 12, 30, 45))
assertEqual(arw.shift(weekday=SU(-1)), arw)
assertEqual(arw.shift(weekday=SU(-2)), arrow.Arrow(2013, 4, 28, 12, 30, 45))

def test_shift_quarters_bug(self):

arw = arrow.Arrow(2013, 5, 5, 12, 30, 45)
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