TST: Fix assertNotIsInstance msg

BUG: Addition raises TypeError if Period is on rhs

Author: sinhrks

doc/source/whatsnew/v0.18.2.txt

@@ -86,7 +86,6 @@ Bug Fixes
 
 
 
-
 - Bug in ``PeriodIndex`` and ``Period`` subtraction raises ``AttributeError`` (:issue:`13071`)
 
 
@@ -103,3 +102,4 @@ Bug Fixes
 
 
 - Bug in ``NaT`` - ``Period`` raises ``AttributeError`` (:issue:`13071`)
+- Bug in ``Period`` addition raises ``TypeError`` if ``Period`` is on right hand side (:issue:`13069`)

pandas/src/period.pyx

@@ -813,16 +813,23 @@ cdef class Period(object):
             return NotImplemented
 
     def __add__(self, other):
-        if isinstance(other, (timedelta, np.timedelta64,
-                              offsets.Tick, offsets.DateOffset, Timedelta)):
-            return self._add_delta(other)
-        elif lib.is_integer(other):
-            if self.ordinal == tslib.iNaT:
-                ordinal = self.ordinal
-            else:
-                ordinal = self.ordinal + other * self.freq.n
-            return Period(ordinal=ordinal, freq=self.freq)
-        else:  # pragma: no cover
+        if isinstance(self, Period):
+            if isinstance(other, (timedelta, np.timedelta64,
+                                  offsets.Tick, offsets.DateOffset, Timedelta)):
+                return self._add_delta(other)
+            elif other is tslib.NaT:
+                return tslib.NaT
+            elif lib.is_integer(other):
+                if self.ordinal == tslib.iNaT:
+                    ordinal = self.ordinal
+                else:
+                    ordinal = self.ordinal + other * self.freq.n
+                return Period(ordinal=ordinal, freq=self.freq)
+            else:  # pragma: no cover
+                return NotImplemented
+        elif isinstance(other, Period):
+            return other + self
+        else:
             return NotImplemented
 
     def __sub__(self, other):

pandas/tseries/offsets.py

@@ -4,7 +4,7 @@
 import numpy as np
 
 from pandas.tseries.tools import to_datetime, normalize_date
-from pandas.core.common import ABCSeries, ABCDatetimeIndex
+from pandas.core.common import ABCSeries, ABCDatetimeIndex, ABCPeriod
 
 # import after tools, dateutil check
 from dateutil.relativedelta import relativedelta, weekday
@@ -381,6 +381,8 @@ def __call__(self, other):
     def __add__(self, other):
         if isinstance(other, (ABCDatetimeIndex, ABCSeries)):
             return other + self
+        elif isinstance(other, ABCPeriod):
+            return other + self
         try:
             return self.apply(other)
         except ApplyTypeError:
@@ -2489,6 +2491,8 @@ def __add__(self, other):
                 return type(self)(self.n + other.n)
             else:
                 return _delta_to_tick(self.delta + other.delta)
+        elif isinstance(other, ABCPeriod):
+            return other + self
         try:
             return self.apply(other)
         except ApplyTypeError: