DOC: update the is_month_start/is_month_end docstring (pandas-dev#23051)

pandas/core/arrays/datetimes.py

@@ -1046,48 +1046,60 @@ def date(self):
         'dim',
         "The number of days in the month")
     daysinmonth = days_in_month
-    is_month_start = _field_accessor(
-        'is_month_start',
-        'is_month_start',
-        "Logical indicating if first day of month (defined by frequency)")
-    is_month_end = _field_accessor(
-        'is_month_end',
-        'is_month_end',
-        """
-        Indicator for whether the date is the last day of the month.
+    _is_month_doc = """
+        Indicates whether the date is the {first_or_last} day of the month.
 
         Returns
         -------
         Series or array
-            For Series, returns a Series with boolean values. For
-            DatetimeIndex, returns a boolean array.
+            For Series, returns a Series with boolean values.
+            For DatetimeIndex, returns a boolean array.
 
         See Also
         --------
-        is_month_start : Indicator for whether the date is the first day
-            of the month.
+        is_month_start : Return a boolean indicating whether the date
+            is the first day of the month.
+        is_month_end : Return a boolean indicating whether the date
+            is the last day of the month.
 
         Examples
         --------
         This method is available on Series with datetime values under
         the ``.dt`` accessor, and directly on DatetimeIndex.
 
-        >>> dates = pd.Series(pd.date_range("2018-02-27", periods=3))
-        >>> dates
+        >>> s = pd.Series(pd.date_range("2018-02-27", periods=3))
+        >>> s
         0   2018-02-27
         1   2018-02-28
         2   2018-03-01
         dtype: datetime64[ns]
-        >>> dates.dt.is_month_end
+        >>> s.dt.is_month_start
+        0    False
+        1    False
+        2    True
+        dtype: bool
+        >>> s.dt.is_month_end
         0    False
         1    True
         2    False
         dtype: bool
 
         >>> idx = pd.date_range("2018-02-27", periods=3)
+        >>> idx.is_month_start
+        array([False, False, True])
         >>> idx.is_month_end
-        array([False,  True, False], dtype=bool)
-        """)
+        array([False, True, False])
+    """
+    is_month_start = _field_accessor(
+        'is_month_start',
+        'is_month_start',
+        _is_month_doc.format(first_or_last='first'))
+
+    is_month_end = _field_accessor(
+        'is_month_end',
+        'is_month_end',
+        _is_month_doc.format(first_or_last='last'))
+
     is_quarter_start = _field_accessor(
         'is_quarter_start',
         'is_quarter_start',