make DateOffset immutable (pandas-dev#21341)

doc/source/whatsnew/v0.24.0.txt

@@ -67,6 +67,7 @@ Datetimelike API Changes
 ^^^^^^^^^^^^^^^^^^^^^^^^
 
 - For :class:`DatetimeIndex` and :class:`TimedeltaIndex` with non-``None`` ``freq`` attribute, addition or subtraction of integer-dtyped array or ``Index`` will return an object of the same class (:issue:`19959`)
+- :class:`DateOffset` objects are now immutable. Attempting to alter one of these will now raise ``AttributeError`` (:issue:`21341`)
 
 .. _whatsnew_0240.api.other:
 
@@ -176,7 +177,6 @@ Timezones
 Offsets
 ^^^^^^^
 
--
 -
 -
 

pandas/_libs/tslibs/offsets.pyx

@@ -304,6 +304,15 @@ class _BaseOffset(object):
     _day_opt = None
     _attributes = frozenset(['n', 'normalize'])
 
+    def __init__(self, n=1, normalize=False):
+        n = self._validate_n(n)
+        object.__setattr__(self, "n", n)
+        object.__setattr__(self, "normalize", normalize)
+        object.__setattr__(self, "_cache", {})
+
+    def __setattr__(self, name, value):
+        raise AttributeError("DateOffset objects are immutable.")
+
     @property
     def kwds(self):
         # for backwards-compatibility
@@ -395,13 +404,14 @@ class _BaseOffset(object):
             kwds = {key: odict[key] for key in odict if odict[key]}
             state.update(kwds)
 
-        self.__dict__ = state
+        self.__dict__.update(state)
+
         if 'weekmask' in state and 'holidays' in state:
             calendar, holidays = _get_calendar(weekmask=self.weekmask,
                                                holidays=self.holidays,
                                                calendar=None)
-            self.calendar = calendar
-            self.holidays = holidays
+            object.__setattr__(self, "calendar", calendar)
+            object.__setattr__(self, "holidays", holidays)
 
     def __getstate__(self):
         """Return a pickleable state"""

pandas/tests/tseries/offsets/test_offsets.py

@@ -234,6 +234,14 @@ class TestCommon(Base):
                  'Nano': Timestamp(np_datetime64_compat(
                                    '2011-01-01T09:00:00.000000001Z'))}
 
+    def test_immutable(self, offset_types):
+        # GH#21341 check that __setattr__ raises
+        offset = self._get_offset(offset_types)
+        with pytest.raises(AttributeError):
+            offset.normalize = True
+        with pytest.raises(AttributeError):
+            offset.n = 91
+
     def test_return_type(self, offset_types):
         offset = self._get_offset(offset_types)
 

pandas/tseries/offsets.py

@@ -23,7 +23,6 @@
     ApplyTypeError,
     as_datetime, _is_normalized,
     _get_calendar, _to_dt64,
-    _determine_offset,
     apply_index_wraps,
     roll_yearday,
     shift_month,
@@ -192,11 +191,14 @@ def __add__(date):
     normalize = False
 
     def __init__(self, n=1, normalize=False, **kwds):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
+        BaseOffset.__init__(self, n, normalize)
 
-        self._offset, self._use_relativedelta = _determine_offset(kwds)
-        self.__dict__.update(kwds)
+        off, use_rd = liboffsets._determine_offset(kwds)
+        object.__setattr__(self, "_offset", off)
+        object.__setattr__(self, "_use_relativedelta", use_rd)
+        for key in kwds:
+            val = kwds[key]
+            object.__setattr__(self, key, val)
 
     @apply_wraps
     def apply(self, other):
@@ -446,9 +448,9 @@ def __init__(self, weekmask, holidays, calendar):
         # following two attributes. See DateOffset._params()
         # holidays, weekmask
 
-        self.weekmask = weekmask
-        self.holidays = holidays
-        self.calendar = calendar
+        object.__setattr__(self, "weekmask", weekmask)
+        object.__setattr__(self, "holidays", holidays)
+        object.__setattr__(self, "calendar", calendar)
 
 
 class BusinessMixin(object):
@@ -480,9 +482,8 @@ class BusinessDay(BusinessMixin, SingleConstructorOffset):
     _attributes = frozenset(['n', 'normalize', 'offset'])
 
     def __init__(self, n=1, normalize=False, offset=timedelta(0)):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
-        self._offset = offset
+        BaseOffset.__init__(self, n, normalize)
+        object.__setattr__(self, "_offset", offset)
 
     def _offset_str(self):
         def get_str(td):
@@ -578,9 +579,11 @@ class BusinessHourMixin(BusinessMixin):
 
     def __init__(self, start='09:00', end='17:00', offset=timedelta(0)):
         # must be validated here to equality check
-        self.start = liboffsets._validate_business_time(start)
-        self.end = liboffsets._validate_business_time(end)
-        self._offset = offset
+        start = liboffsets._validate_business_time(start)
+        object.__setattr__(self, "start", start)
+        end = liboffsets._validate_business_time(end)
+        object.__setattr__(self, "end", end)
+        object.__setattr__(self, "_offset", offset)
 
     @cache_readonly
     def next_bday(self):
@@ -807,8 +810,7 @@ class BusinessHour(BusinessHourMixin, SingleConstructorOffset):
 
     def __init__(self, n=1, normalize=False, start='09:00',
                  end='17:00', offset=timedelta(0)):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
+        BaseOffset.__init__(self, n, normalize)
         super(BusinessHour, self).__init__(start=start, end=end, offset=offset)
 
 
@@ -837,9 +839,8 @@ class CustomBusinessDay(_CustomMixin, BusinessDay):
 
     def __init__(self, n=1, normalize=False, weekmask='Mon Tue Wed Thu Fri',
                  holidays=None, calendar=None, offset=timedelta(0)):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
-        self._offset = offset
+        BaseOffset.__init__(self, n, normalize)
+        object.__setattr__(self, "_offset", offset)
 
         _CustomMixin.__init__(self, weekmask, holidays, calendar)
 
@@ -898,9 +899,8 @@ class CustomBusinessHour(_CustomMixin, BusinessHourMixin,
     def __init__(self, n=1, normalize=False, weekmask='Mon Tue Wed Thu Fri',
                  holidays=None, calendar=None,
                  start='09:00', end='17:00', offset=timedelta(0)):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
-        self._offset = offset
+        BaseOffset.__init__(self, n, normalize)
+        object.__setattr__(self, "_offset", offset)
 
         _CustomMixin.__init__(self, weekmask, holidays, calendar)
         BusinessHourMixin.__init__(self, start=start, end=end, offset=offset)
@@ -914,9 +914,7 @@ class MonthOffset(SingleConstructorOffset):
     _adjust_dst = True
     _attributes = frozenset(['n', 'normalize'])
 
-    def __init__(self, n=1, normalize=False):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
+    __init__ = BaseOffset.__init__
 
     @property
     def name(self):
@@ -995,9 +993,8 @@ class _CustomBusinessMonth(_CustomMixin, BusinessMixin, MonthOffset):
 
     def __init__(self, n=1, normalize=False, weekmask='Mon Tue Wed Thu Fri',
                  holidays=None, calendar=None, offset=timedelta(0)):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
-        self._offset = offset
+        BaseOffset.__init__(self, n, normalize)
+        object.__setattr__(self, "_offset", offset)
 
         _CustomMixin.__init__(self, weekmask, holidays, calendar)
 
@@ -1074,18 +1071,18 @@ class SemiMonthOffset(DateOffset):
     _attributes = frozenset(['n', 'normalize', 'day_of_month'])
 
     def __init__(self, n=1, normalize=False, day_of_month=None):
+        BaseOffset.__init__(self, n, normalize)
+
         if day_of_month is None:
-            self.day_of_month = self._default_day_of_month
+            object.__setattr__(self, "day_of_month",
+                               self._default_day_of_month)
         else:
-            self.day_of_month = int(day_of_month)
+            object.__setattr__(self, "day_of_month", int(day_of_month))
         if not self._min_day_of_month <= self.day_of_month <= 27:
             msg = 'day_of_month must be {min}<=day_of_month<=27, got {day}'
             raise ValueError(msg.format(min=self._min_day_of_month,
                                         day=self.day_of_month))
 
-        self.n = self._validate_n(n)
-        self.normalize = normalize
-
     @classmethod
     def _from_name(cls, suffix=None):
         return cls(day_of_month=suffix)
@@ -1291,9 +1288,8 @@ class Week(DateOffset):
     _attributes = frozenset(['n', 'normalize', 'weekday'])
 
     def __init__(self, n=1, normalize=False, weekday=None):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
-        self.weekday = weekday
+        BaseOffset.__init__(self, n, normalize)
+        object.__setattr__(self, "weekday", weekday)
 
         if self.weekday is not None:
             if self.weekday < 0 or self.weekday > 6:
@@ -1421,10 +1417,9 @@ class WeekOfMonth(_WeekOfMonthMixin, DateOffset):
     _attributes = frozenset(['n', 'normalize', 'week', 'weekday'])
 
     def __init__(self, n=1, normalize=False, week=0, weekday=0):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
-        self.weekday = weekday
-        self.week = week
+        BaseOffset.__init__(self, n, normalize)
+        object.__setattr__(self, "weekday", weekday)
+        object.__setattr__(self, "week", week)
 
         if self.weekday < 0 or self.weekday > 6:
             raise ValueError('Day must be 0<=day<=6, got {day}'
@@ -1493,9 +1488,8 @@ class LastWeekOfMonth(_WeekOfMonthMixin, DateOffset):
     _attributes = frozenset(['n', 'normalize', 'weekday'])
 
     def __init__(self, n=1, normalize=False, weekday=0):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
-        self.weekday = weekday
+        BaseOffset.__init__(self, n, normalize)
+        object.__setattr__(self, "weekday", weekday)
 
         if self.n == 0:
             raise ValueError('N cannot be 0')
@@ -1553,11 +1547,11 @@ class QuarterOffset(DateOffset):
     #       startingMonth vs month attr names are resolved
 
     def __init__(self, n=1, normalize=False, startingMonth=None):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
+        BaseOffset.__init__(self, n, normalize)
+
         if startingMonth is None:
             startingMonth = self._default_startingMonth
-        self.startingMonth = startingMonth
+        object.__setattr__(self, "startingMonth", startingMonth)
 
     def isAnchored(self):
         return (self.n == 1 and self.startingMonth is not None)
@@ -1679,11 +1673,10 @@ def onOffset(self, dt):
         return dt.month == self.month and dt.day == self._get_offset_day(dt)
 
     def __init__(self, n=1, normalize=False, month=None):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
+        BaseOffset.__init__(self, n, normalize)
 
         month = month if month is not None else self._default_month
-        self.month = month
+        object.__setattr__(self, "month", month)
 
         if self.month < 1 or self.month > 12:
             raise ValueError('Month must go from 1 to 12')
@@ -1776,12 +1769,11 @@ class FY5253(DateOffset):
 
     def __init__(self, n=1, normalize=False, weekday=0, startingMonth=1,
                  variation="nearest"):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
-        self.startingMonth = startingMonth
-        self.weekday = weekday
+        BaseOffset.__init__(self, n, normalize)
+        object.__setattr__(self, "startingMonth", startingMonth)
+        object.__setattr__(self, "weekday", weekday)
 
-        self.variation = variation
+        object.__setattr__(self, "variation", variation)
 
         if self.n == 0:
             raise ValueError('N cannot be 0')
@@ -1976,13 +1968,12 @@ class FY5253Quarter(DateOffset):
 
     def __init__(self, n=1, normalize=False, weekday=0, startingMonth=1,
                  qtr_with_extra_week=1, variation="nearest"):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
+        BaseOffset.__init__(self, n, normalize)
 
-        self.weekday = weekday
-        self.startingMonth = startingMonth
-        self.qtr_with_extra_week = qtr_with_extra_week
-        self.variation = variation
+        object.__setattr__(self, "startingMonth", startingMonth)
+        object.__setattr__(self, "weekday", weekday)
+        object.__setattr__(self, "qtr_with_extra_week", qtr_with_extra_week)
+        object.__setattr__(self, "variation", variation)
 
         if self.n == 0:
             raise ValueError('N cannot be 0')
@@ -2129,9 +2120,7 @@ class Easter(DateOffset):
     _adjust_dst = True
     _attributes = frozenset(['n', 'normalize'])
 
-    def __init__(self, n=1, normalize=False):
-        self.n = self._validate_n(n)
-        self.normalize = normalize
+    __init__ = BaseOffset.__init__
 
     @apply_wraps
     def apply(self, other):
@@ -2177,11 +2166,10 @@ class Tick(SingleConstructorOffset):
     _attributes = frozenset(['n', 'normalize'])
 
     def __init__(self, n=1, normalize=False):
-        self.n = self._validate_n(n)
+        BaseOffset.__init__(self, n, normalize)
         if normalize:
             raise ValueError("Tick offset with `normalize=True` are not "
                              "allowed.")  # GH#21427
-        self.normalize = normalize
 
     __gt__ = _tick_comp(operator.gt)
     __ge__ = _tick_comp(operator.ge)