From 53a877a22c24df4a51228c23395e68b98df147bd Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Sat, 4 Jan 2020 09:11:50 -0800
Subject: [PATCH] Fix PeriodIndex.get_indexer with non-PI

---
 pandas/core/indexes/period.py                | 24 ++++++----------
 pandas/tests/indexes/period/test_indexing.py | 29 ++++++++++++++++++++
 2 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/pandas/core/indexes/period.py b/pandas/core/indexes/period.py
index 1cc37504b675f..363ff32519d27 100644
--- a/pandas/core/indexes/period.py
+++ b/pandas/core/indexes/period.py
@@ -564,15 +564,12 @@ def get_value(self, series, key):
     def get_indexer(self, target, method=None, limit=None, tolerance=None):
         target = ensure_index(target)
 
-        if hasattr(target, "freq") and target.freq != self.freq:
-            msg = DIFFERENT_FREQ.format(
-                cls=type(self).__name__,
-                own_freq=self.freqstr,
-                other_freq=target.freqstr,
-            )
-            raise IncompatibleFrequency(msg)
-
         if isinstance(target, PeriodIndex):
+            if target.freq != self.freq:
+                # No matches
+                no_matches = -1 * np.ones(self.shape, dtype=np.intp)
+                return no_matches
+
             target = target.asi8
             self_index = self._int64index
         else:
@@ -587,14 +584,11 @@ def get_indexer_non_unique(self, target):
         target = ensure_index(target)
 
         if isinstance(target, PeriodIndex):
+            if target.freq != self.freq:
+                no_matches = -1 * np.ones(self.shape, dtype=np.intp)
+                return no_matches, no_matches
+
             target = target.asi8
-            if hasattr(target, "freq") and target.freq != self.freq:
-                msg = DIFFERENT_FREQ.format(
-                    cls=type(self).__name__,
-                    own_freq=self.freqstr,
-                    other_freq=target.freqstr,
-                )
-                raise IncompatibleFrequency(msg)
 
         indexer, missing = self._int64index.get_indexer_non_unique(target)
         return ensure_platform_int(indexer), missing
diff --git a/pandas/tests/indexes/period/test_indexing.py b/pandas/tests/indexes/period/test_indexing.py
index 8b5a2958c4c61..e95b4ae5397b4 100644
--- a/pandas/tests/indexes/period/test_indexing.py
+++ b/pandas/tests/indexes/period/test_indexing.py
@@ -550,6 +550,35 @@ def test_get_indexer(self):
         res = idx.get_indexer(target, "nearest", tolerance=pd.Timedelta("1 day"))
         tm.assert_numpy_array_equal(res, np.array([0, 0, 1, -1], dtype=np.intp))
 
+    def test_get_indexer_mismatched_dtype(self):
+        # Check that we return all -1s and do not raise or cast incorrectly
+
+        dti = pd.date_range("2016-01-01", periods=3)
+        pi = dti.to_period("D")
+        pi2 = dti.to_period("W")
+
+        expected = np.array([-1, -1, -1], dtype=np.intp)
+
+        result = pi.get_indexer(dti)
+        tm.assert_numpy_array_equal(result, expected)
+
+        # This should work in both directions
+        result = dti.get_indexer(pi)
+        tm.assert_numpy_array_equal(result, expected)
+
+        result = pi.get_indexer(pi2)
+        tm.assert_numpy_array_equal(result, expected)
+
+        # We expect the same from get_indexer_non_unique
+        result = pi.get_indexer_non_unique(dti)[0]
+        tm.assert_numpy_array_equal(result, expected)
+
+        result = dti.get_indexer_non_unique(pi)[0]
+        tm.assert_numpy_array_equal(result, expected)
+
+        result = pi.get_indexer_non_unique(pi2)[0]
+        tm.assert_numpy_array_equal(result, expected)
+
     def test_get_indexer_non_unique(self):
         # GH 17717
         p1 = pd.Period("2017-09-02")