REF: inherit BaseOffset in WeekOfMonthMixin (#34184)

Author: jbrockmendel

pandas/_libs/tslibs/offsets.pyx

@@ -23,7 +23,7 @@ from pandas._libs.tslibs.util cimport is_integer_object, is_datetime64_object
 
 from pandas._libs.tslibs.base cimport ABCTick, ABCTimestamp, is_tick_object
 
-from pandas._libs.tslibs.ccalendar import MONTHS, DAYS
+from pandas._libs.tslibs.ccalendar import MONTHS, DAYS, weekday_to_int, int_to_weekday
 from pandas._libs.tslibs.ccalendar cimport get_days_in_month, dayofweek
 from pandas._libs.tslibs.conversion cimport (
     convert_datetime_to_tsobject,
@@ -986,10 +986,16 @@ class CustomMixin:
         object.__setattr__(self, "calendar", calendar)
 
 
-class WeekOfMonthMixin:
+class WeekOfMonthMixin(BaseOffset):
     """
     Mixin for methods common to WeekOfMonth and LastWeekOfMonth.
     """
+    def __init__(self, n=1, normalize=False, weekday=0):
+        BaseOffset.__init__(self, n, normalize)
+        object.__setattr__(self, "weekday", weekday)
+
+        if weekday < 0 or weekday > 6:
+            raise ValueError(f"Day must be 0<=day<=6, got {weekday}")
 
     @apply_wraps
     def apply(self, other):
@@ -1010,6 +1016,14 @@ class WeekOfMonthMixin:
             return False
         return dt.day == self._get_offset_day(dt)
 
+    @property
+    def rule_code(self) -> str:
+        weekday = int_to_weekday.get(self.weekday, "")
+        if self.week == -1:
+            # LastWeekOfMonth
+            return f"{self._prefix}-{weekday}"
+        return f"{self._prefix}-{self.week + 1}{weekday}"
+
 
 # ----------------------------------------------------------------------
 # RelativeDelta Arithmetic

pandas/tseries/frequencies.py

@@ -165,7 +165,7 @@ def to_offset(freq) -> Optional[DateOffset]:
                     )
                 stride = int(stride)
                 offset = _get_offset(name)
-                offset = offset * int(np.fabs(stride) * stride_sign)
+                offset = offset * int(np.fabs(stride) * stride_sign)  # type: ignore
                 if delta is None:
                     delta = offset
                 else:

pandas/tseries/offsets.py

@@ -296,7 +296,7 @@ def is_on_offset(self, dt):
         return True
 
 
-class SingleConstructorOffset(BaseOffset):
+class SingleConstructorMixin:
     _params = cache_readonly(BaseOffset._params.fget)
     freqstr = cache_readonly(BaseOffset.freqstr.fget)
 
@@ -308,6 +308,10 @@ def _from_name(cls, suffix=None):
         return cls()
 
 
+class SingleConstructorOffset(SingleConstructorMixin, BaseOffset):
+    pass
+
+
 class BusinessDay(BusinessMixin, SingleConstructorOffset):
     """
     DateOffset subclass representing possibly n business days.
@@ -1308,7 +1312,7 @@ def _from_name(cls, suffix=None):
         return cls(weekday=weekday)
 
 
-class WeekOfMonth(liboffsets.WeekOfMonthMixin, SingleConstructorOffset):
+class WeekOfMonth(SingleConstructorMixin, liboffsets.WeekOfMonthMixin):
     """
     Describes monthly dates like "the Tuesday of the 2nd week of each month".
 
@@ -1334,12 +1338,9 @@ class WeekOfMonth(liboffsets.WeekOfMonthMixin, SingleConstructorOffset):
     _attributes = frozenset(["n", "normalize", "week", "weekday"])
 
     def __init__(self, n=1, normalize=False, week=0, weekday=0):
-        BaseOffset.__init__(self, n, normalize)
-        object.__setattr__(self, "weekday", weekday)
+        liboffsets.WeekOfMonthMixin.__init__(self, n, normalize, weekday)
         object.__setattr__(self, "week", week)
 
-        if self.weekday < 0 or self.weekday > 6:
-            raise ValueError(f"Day must be 0<=day<=6, got {self.weekday}")
         if self.week < 0 or self.week > 3:
             raise ValueError(f"Week must be 0<=week<=3, got {self.week}")
 
@@ -1361,11 +1362,6 @@ def _get_offset_day(self, other: datetime) -> int:
         shift_days = (self.weekday - wday) % 7
         return 1 + shift_days + self.week * 7
 
-    @property
-    def rule_code(self) -> str:
-        weekday = ccalendar.int_to_weekday.get(self.weekday, "")
-        return f"{self._prefix}-{self.week + 1}{weekday}"
-
     @classmethod
     def _from_name(cls, suffix=None):
         if not suffix:
@@ -1377,7 +1373,7 @@ def _from_name(cls, suffix=None):
         return cls(week=week, weekday=weekday)
 
 
-class LastWeekOfMonth(liboffsets.WeekOfMonthMixin, SingleConstructorOffset):
+class LastWeekOfMonth(SingleConstructorMixin, liboffsets.WeekOfMonthMixin):
     """
     Describes monthly dates in last week of month like "the last Tuesday of
     each month".
@@ -1401,14 +1397,11 @@ class LastWeekOfMonth(liboffsets.WeekOfMonthMixin, SingleConstructorOffset):
     _attributes = frozenset(["n", "normalize", "weekday"])
 
     def __init__(self, n=1, normalize=False, weekday=0):
-        BaseOffset.__init__(self, n, normalize)
-        object.__setattr__(self, "weekday", weekday)
+        liboffsets.WeekOfMonthMixin.__init__(self, n, normalize, weekday)
 
         if self.n == 0:
             raise ValueError("N cannot be 0")
-
-        if self.weekday < 0 or self.weekday > 6:
-            raise ValueError(f"Day must be 0<=day<=6, got {self.weekday}")
+        object.__setattr__(self, "week", -1)
 
     def _get_offset_day(self, other: datetime) -> int:
         """
@@ -1429,11 +1422,6 @@ def _get_offset_day(self, other: datetime) -> int:
         shift_days = (wday - self.weekday) % 7
         return dim - shift_days
 
-    @property
-    def rule_code(self) -> str:
-        weekday = ccalendar.int_to_weekday.get(self.weekday, "")
-        return f"{self._prefix}-{weekday}"
-
     @classmethod
     def _from_name(cls, suffix=None):
         if not suffix: