REF: make MonthOffset a cdef class (#34324)

Author: jbrockmendel

doc/source/reference/offset_frequency.rst

@@ -173,40 +173,6 @@ Methods
     CustomBusinessHour.is_on_offset
     CustomBusinessHour.__call__
 
-MonthOffset
------------
-.. autosummary::
-   :toctree: api/
-
-    MonthOffset
-
-Properties
-~~~~~~~~~~
-.. autosummary::
-   :toctree: api/
-
-    MonthOffset.freqstr
-    MonthOffset.kwds
-    MonthOffset.name
-    MonthOffset.nanos
-    MonthOffset.normalize
-    MonthOffset.rule_code
-    MonthOffset.n
-
-Methods
-~~~~~~~
-.. autosummary::
-   :toctree: api/
-
-    MonthOffset.apply
-    MonthOffset.apply_index
-    MonthOffset.copy
-    MonthOffset.isAnchored
-    MonthOffset.onOffset
-    MonthOffset.is_anchored
-    MonthOffset.is_on_offset
-    MonthOffset.__call__
-
 MonthEnd
 --------
 .. autosummary::

pandas/_libs/tslibs/offsets.pyx

@@ -1299,6 +1299,31 @@ cdef class QuarterOffset(BaseOffset):
         return type(dtindex)._simple_new(shifted, dtype=dtindex.dtype)
 
 
+cdef class MonthOffset(BaseOffset):
+    def is_on_offset(self, dt) -> bool:
+        if self.normalize and not is_normalized(dt):
+            return False
+        return dt.day == self._get_offset_day(dt)
+
+    @apply_wraps
+    def apply(self, other):
+        compare_day = self._get_offset_day(other)
+        n = roll_convention(other.day, self.n, compare_day)
+        return shift_month(other, n, self._day_opt)
+
+    @apply_index_wraps
+    def apply_index(self, dtindex):
+        shifted = shift_months(dtindex.asi8, self.n, self._day_opt)
+        return type(dtindex)._simple_new(shifted, dtype=dtindex.dtype)
+
+    @classmethod
+    def _from_name(cls, suffix=None):
+        # default _from_name calls cls with no args
+        if suffix:
+            raise ValueError(f"Bad freq suffix {suffix}")
+        return cls()
+
+
 # ----------------------------------------------------------------------
 # RelativeDelta Arithmetic
 

pandas/tests/tseries/offsets/conftest.py

@@ -1,5 +1,7 @@
 import pytest
 
+from pandas._libs.tslibs.offsets import MonthOffset
+
 import pandas.tseries.offsets as offsets
 
 
@@ -15,7 +17,7 @@ def offset_types(request):
     params=[
         getattr(offsets, o)
         for o in offsets.__all__
-        if issubclass(getattr(offsets, o), offsets.MonthOffset) and o != "MonthOffset"
+        if issubclass(getattr(offsets, o), MonthOffset) and o != "MonthOffset"
     ]
 )
 def month_classes(request):

pandas/tseries/offsets.py

@@ -820,25 +820,7 @@ def __init__(
 # Month-Based Offset Classes
 
 
-class MonthOffset(SingleConstructorOffset):
-    def is_on_offset(self, dt: datetime) -> bool:
-        if self.normalize and not is_normalized(dt):
-            return False
-        return dt.day == self._get_offset_day(dt)
-
-    @apply_wraps
-    def apply(self, other):
-        compare_day = self._get_offset_day(other)
-        n = liboffsets.roll_convention(other.day, self.n, compare_day)
-        return shift_month(other, n, self._day_opt)
-
-    @apply_index_wraps
-    def apply_index(self, i):
-        shifted = liboffsets.shift_months(i.asi8, self.n, self._day_opt)
-        return type(i)._simple_new(shifted, dtype=i.dtype)
-
-
-class MonthEnd(MonthOffset):
+class MonthEnd(SingleConstructorMixin, liboffsets.MonthOffset):
     """
     DateOffset of one month end.
     """
@@ -847,7 +829,7 @@ class MonthEnd(MonthOffset):
     _day_opt = "end"
 
 
-class MonthBegin(MonthOffset):
+class MonthBegin(SingleConstructorMixin, liboffsets.MonthOffset):
     """
     DateOffset of one month at beginning.
     """
@@ -856,7 +838,7 @@ class MonthBegin(MonthOffset):
     _day_opt = "start"
 
 
-class BusinessMonthEnd(MonthOffset):
+class BusinessMonthEnd(SingleConstructorMixin, liboffsets.MonthOffset):
     """
     DateOffset increments between business EOM dates.
     """
@@ -865,7 +847,7 @@ class BusinessMonthEnd(MonthOffset):
     _day_opt = "business_end"
 
 
-class BusinessMonthBegin(MonthOffset):
+class BusinessMonthBegin(SingleConstructorMixin, liboffsets.MonthOffset):
     """
     DateOffset of one business month at beginning.
     """
@@ -875,7 +857,9 @@ class BusinessMonthBegin(MonthOffset):
 
 
 @doc(bound="bound")
-class _CustomBusinessMonth(CustomMixin, BusinessMixin, MonthOffset):
+class _CustomBusinessMonth(
+    CustomMixin, BusinessMixin, SingleConstructorMixin, liboffsets.MonthOffset
+):
     """
     DateOffset subclass representing custom business month(s).