BUG - remove scaling multiplier from Period diff result

doc/source/whatsnew/v0.24.0.rst

@@ -1056,7 +1056,7 @@ from :class:`Period`, :class:`PeriodIndex`, and in some cases
 :class:`Timestamp`, :class:`DatetimeIndex` and :class:`TimedeltaIndex`.
 
 This usage is now deprecated.  Instead add or subtract integer multiples of
-the object's ``freq`` attribute (:issue:`21939`)
+the object's ``freq`` attribute (:issue:`21939`) / (:issue:`23878`)
 
 Previous Behavior:
 

pandas/_libs/tslibs/period.pyx

@@ -1685,7 +1685,9 @@ cdef class _Period(object):
                 if other.freq != self.freq:
                     msg = _DIFFERENT_FREQ.format(self.freqstr, other.freqstr)
                     raise IncompatibleFrequency(msg)
-                return (self.ordinal - other.ordinal) * self.freq
+                base_freq = type(self.freq)(normalize=self.freq.normalize,
+                                            **self.freq.kwds)
+                return (self.ordinal - other.ordinal) * base_freq
             elif getattr(other, '_typ', None) == 'periodindex':
                 # GH#21314 PeriodIndex - Period returns an object-index
                 # of DateOffset objects, for which we cannot use __neg__

pandas/tests/scalar/period/test_period.py

@@ -1106,6 +1106,38 @@ def test_sub(self):
         with pytest.raises(period.IncompatibleFrequency, match=msg):
             per1 - Period('2011-02', freq='M')
 
+    @pytest.mark.parametrize('kwds', [
+        {},
+        {'normalize': True},
+        {'normalize': False},
+        {'normalize': True, 'month': 4},
+        {'normalize': False, 'month': 4},
+    ])
+    @pytest.mark.parametrize('n', [1, 2, 3, 4])
+    @pytest.mark.parametrize('freq,expected', [
+        (pd.offsets.Second, 18489600),
+        (pd.offsets.Minute, 308160),
+        (pd.offsets.Hour, 5136),
+        (pd.offsets.Day, 214),
+        (pd.offsets.MonthEnd, 7),
+        (pd.offsets.YearEnd, 1),
+    ])
+    def test_sub_non_standard_freq(self, freq, expected, n, kwds):
+        # GH 23878
+        # Only kwd allowed in period compatible freqs is 'month' in `YearEnd`
+        if 'month' in kwds:
+            if freq is pd.offsets.YearEnd:
+                expected = 0
+            else:
+                return
+        # Only non-Tick frequencies can have normalize set to True
+        if pd.tseries.offsets.Tick in freq.__bases__ and kwds.get('normalize'):
+            return
+
+        p1 = pd.Period('19910905', freq=freq(n, **kwds))
+        p2 = pd.Period('19920406', freq=freq(n, **kwds))
+        assert (p2 - p1) == freq(expected, **kwds)
+
     def test_add_offset(self):
         # freq is DateOffset
         for freq in ['A', '2A', '3A']: