DOC: use substitution decorator for business month classes (pandas-dev#25828)

Author: Batalex

doc/source/whatsnew/v0.25.0.rst

@@ -35,6 +35,7 @@ Other Enhancements
 - :class:`RangeIndex` has gained :attr:`~RangeIndex.start`, :attr:`~RangeIndex.stop`, and :attr:`~RangeIndex.step` attributes (:issue:`25710`)
 - :class:`datetime.timezone` objects are now supported as arguments to timezone methods and constructors (:issue:`25065`)
 - :meth:`DataFrame.query` and :meth:`DataFrame.eval` now supports quoting column names with backticks to refer to names with spaces (:issue:`6508`)
+- :class:`CustomBusinessMonthBegin` and :class:`CustomBusinessMonthEnd` now use the substitution pattern for docstring sharing
 
 .. _whatsnew_0250.api_breaking:
 

pandas/tseries/offsets.py

@@ -16,7 +16,7 @@
 import pandas.compat as compat
 from pandas.compat import range
 from pandas.errors import AbstractMethodError
-from pandas.util._decorators import cache_readonly
+from pandas.util._decorators import cache_readonly, Substitution, Appender
 
 from pandas.core.dtypes.generic import ABCPeriod
 
@@ -973,7 +973,7 @@ class BusinessMonthBegin(MonthOffset):
 class _CustomBusinessMonth(_CustomMixin, BusinessMixin, MonthOffset):
     """
     DateOffset subclass representing one custom business month, incrementing
-    between [BEGIN/END] of month dates.
+    between %(bound)s of month dates.
 
     Parameters
     ----------
@@ -1053,18 +1053,15 @@ def apply(self, other):
         return result
 
 
+@Substitution(bound="end")
+@Appender(_CustomBusinessMonth.__doc__)
 class CustomBusinessMonthEnd(_CustomBusinessMonth):
-    # TODO(py27): Replace condition with Subsitution after dropping Py27
-    if _CustomBusinessMonth.__doc__:
-        __doc__ = _CustomBusinessMonth.__doc__.replace('[BEGIN/END]', 'end')
     _prefix = 'CBM'
 
 
+@Substitution(bound="beginning")
+@Appender(_CustomBusinessMonth.__doc__)
 class CustomBusinessMonthBegin(_CustomBusinessMonth):
-    # TODO(py27): Replace condition with Subsitution after dropping Py27
-    if _CustomBusinessMonth.__doc__:
-        __doc__ = _CustomBusinessMonth.__doc__.replace('[BEGIN/END]',
-                                                       'beginning')
     _prefix = 'CBMS'