REF: _validate_foo pattern for IntervalArray (#36414)

Author: jbrockmendel

pandas/core/arrays/interval.py

@@ -640,17 +640,10 @@ def fillna(self, value=None, method=None, limit=None):
         if limit is not None:
             raise TypeError("limit is not supported for IntervalArray.")
 
-        if not isinstance(value, Interval):
-            msg = (
-                "'IntervalArray.fillna' only supports filling with a "
-                f"scalar 'pandas.Interval'. Got a '{type(value).__name__}' instead."
-            )
-            raise TypeError(msg)
-
-        self._check_closed_matches(value, name="value")
+        value_left, value_right = self._validate_fillna_value(value)
 
-        left = self.left.fillna(value=value.left)
-        right = self.right.fillna(value=value.right)
+        left = self.left.fillna(value=value_left)
+        right = self.right.fillna(value=value_right)
         return self._shallow_copy(left, right)
 
     @property
@@ -845,18 +838,7 @@ def take(self, indices, allow_fill=False, fill_value=None, axis=None, **kwargs):
 
         fill_left = fill_right = fill_value
         if allow_fill:
-            if fill_value is None:
-                fill_left = fill_right = self.left._na_value
-            elif is_interval(fill_value):
-                self._check_closed_matches(fill_value, name="fill_value")
-                fill_left, fill_right = fill_value.left, fill_value.right
-            elif not is_scalar(fill_value) and notna(fill_value):
-                msg = (
-                    "'IntervalArray.fillna' only supports filling with a "
-                    "'scalar pandas.Interval or NA'. "
-                    f"Got a '{type(fill_value).__name__}' instead."
-                )
-                raise ValueError(msg)
+            fill_left, fill_right = self._validate_fill_value(fill_value)
 
         left_take = take(
             self.left, indices, allow_fill=allow_fill, fill_value=fill_left
@@ -867,6 +849,49 @@ def take(self, indices, allow_fill=False, fill_value=None, axis=None, **kwargs):
 
         return self._shallow_copy(left_take, right_take)
 
+    def _validate_fill_value(self, value):
+        if is_interval(value):
+            self._check_closed_matches(value, name="fill_value")
+            fill_left, fill_right = value.left, value.right
+        elif not is_scalar(value) and notna(value):
+            msg = (
+                "'IntervalArray.fillna' only supports filling with a "
+                "'scalar pandas.Interval or NA'. "
+                f"Got a '{type(value).__name__}' instead."
+            )
+            raise ValueError(msg)
+        else:
+            fill_left = fill_right = self.left._na_value
+        return fill_left, fill_right
+
+    def _validate_fillna_value(self, value):
+        if not isinstance(value, Interval):
+            msg = (
+                "'IntervalArray.fillna' only supports filling with a "
+                f"scalar 'pandas.Interval'. Got a '{type(value).__name__}' instead."
+            )
+            raise TypeError(msg)
+
+        self._check_closed_matches(value, name="value")
+        return value.left, value.right
+
+    def _validate_insert_value(self, value):
+        if isinstance(value, Interval):
+            if value.closed != self.closed:
+                raise ValueError(
+                    "inserted item must be closed on the same side as the index"
+                )
+            left_insert = value.left
+            right_insert = value.right
+        elif is_scalar(value) and isna(value):
+            # GH#18295
+            left_insert = right_insert = value
+        else:
+            raise ValueError(
+                "can only insert Interval objects and NA into an IntervalIndex"
+            )
+        return left_insert, right_insert
+
     def value_counts(self, dropna=True):
         """
         Returns a Series containing counts of each interval.

pandas/core/indexes/interval.py

@@ -333,7 +333,9 @@ def from_tuples(
     # --------------------------------------------------------------------
 
     @Appender(Index._shallow_copy.__doc__)
-    def _shallow_copy(self, values=None, name: Label = lib.no_default):
+    def _shallow_copy(
+        self, values: Optional[IntervalArray] = None, name: Label = lib.no_default
+    ):
         name = self.name if name is lib.no_default else name
         cache = self._cache.copy() if values is None else {}
         if values is None:
@@ -927,20 +929,7 @@ def insert(self, loc, item):
         -------
         IntervalIndex
         """
-        if isinstance(item, Interval):
-            if item.closed != self.closed:
-                raise ValueError(
-                    "inserted item must be closed on the same side as the index"
-                )
-            left_insert = item.left
-            right_insert = item.right
-        elif is_scalar(item) and isna(item):
-            # GH 18295
-            left_insert = right_insert = item
-        else:
-            raise ValueError(
-                "can only insert Interval objects and NA into an IntervalIndex"
-            )
+        left_insert, right_insert = self._data._validate_insert_value(item)
 
         new_left = self.left.insert(loc, left_insert)
         new_right = self.right.insert(loc, right_insert)