BUG: Do not use string Index like Datetimelike Index

Author: nrebena

pandas/core/indexes/datetimelike.py

@@ -142,13 +142,16 @@ def equals(self, other) -> bool:
         if not isinstance(other, ABCIndexClass):
             return False
         elif not isinstance(other, type(self)):
-            try:
-                other = type(self)(other)
-            except (ValueError, TypeError, OverflowError):
-                # e.g.
-                #  ValueError -> cannot parse str entry, or OutOfBoundsDatetime
-                #  TypeError  -> trying to convert IntervalIndex to DatetimeIndex
-                #  OverflowError -> Index([very_large_timedeltas])
+            if self._is_convertible_to_index_for_join(other):
+                try:
+                    other = type(self)(other)
+                except (ValueError, TypeError, OverflowError):
+                    # e.g.
+                    #  ValueError -> cannot parse str entry, or OutOfBoundsDatetime
+                    #  TypeError  -> trying to convert IntervalIndex to DatetimeIndex
+                    #  OverflowError -> Index([very_large_timedeltas])
+                    return False
+            else:
                 return False
 
         if not is_dtype_equal(self.dtype, other.dtype):
@@ -602,6 +605,26 @@ def delete(self, loc):
         arr = type(self._data)._simple_new(new_i8s, dtype=self.dtype, freq=freq)
         return type(self)._simple_new(arr, name=self.name)
 
+    @classmethod
+    def _is_convertible_to_index_for_join(cls, other: Index) -> bool:
+        """
+        return a boolean whether I can attempt conversion to a
+        DatetimeIndex/TimedeltaIndex
+        """
+        if isinstance(other, cls):
+            return False
+        elif len(other) > 0 and other.inferred_type not in (
+            "floating",
+            "mixed-integer",
+            "integer",
+            "integer-na",
+            "mixed-integer-float",
+            "mixed",
+            "string",
+        ):
+            return True
+        return False
+
 
 class DatetimeTimedeltaMixin(DatetimeIndexOpsMixin, Int64Index):
     """
@@ -873,25 +896,6 @@ def _maybe_utc_convert(self, other):
                 other = other.tz_convert("UTC")
         return this, other
 
-    @classmethod
-    def _is_convertible_to_index_for_join(cls, other: Index) -> bool:
-        """
-        return a boolean whether I can attempt conversion to a
-        DatetimeIndex/TimedeltaIndex
-        """
-        if isinstance(other, cls):
-            return False
-        elif len(other) > 0 and other.inferred_type not in (
-            "floating",
-            "mixed-integer",
-            "integer",
-            "integer-na",
-            "mixed-integer-float",
-            "mixed",
-        ):
-            return True
-        return False
-
     def _wrap_joined_index(self, joined: np.ndarray, other):
         assert other.dtype == self.dtype, (other.dtype, self.dtype)
         name = get_op_result_name(self, other)

pandas/tests/indexes/datetimes/test_misc.py

@@ -373,3 +373,20 @@ def test_iter_readonly():
     arr.setflags(write=False)
     dti = pd.to_datetime(arr)
     list(dti)
+
+
+def test_datetimelike_string():
+    # Related to PR 32739
+    # Ensure we do not compare strings and datetimelike type.
+    date_string = "2020-04-13"
+    i1 = pd.Index([date_string])
+    i2 = pd.Index([pd.to_datetime(date_string)])
+
+    assert i1.equals(i2) is False
+    assert i2.equals(i1) is False
+
+    assert len(i1.intersection(i2)) == 0
+    assert len(i2.intersection(i1)) == 0
+
+    assert len(i1.union(i2)) == 2
+    assert len(i2.union(i1)) == 2