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doc/source/user_guide/categorical.rst

@@ -777,8 +777,8 @@ value is included in the ``categories``:
     df
     try:
         df.iloc[2:4, :] = [["c", 3], ["c", 3]]
-    except ValueError as e:
-        print("ValueError:", str(e))
+    except TypeError as e:
+        print("TypeError:", str(e))
 
 Setting values by assigning categorical data will also check that the ``categories`` match:
 
@@ -788,8 +788,8 @@ Setting values by assigning categorical data will also check that the ``categori
     df
     try:
         df.loc["j":"k", "cats"] = pd.Categorical(["b", "b"], categories=["a", "b", "c"])
-    except ValueError as e:
-        print("ValueError:", str(e))
+    except TypeError as e:
+        print("TypeError:", str(e))
 
 Assigning a ``Categorical`` to parts of a column of other types will use the values:
 

doc/source/user_guide/groupby.rst

@@ -391,7 +391,6 @@ something different for each of the columns. Thus, using ``[]`` similar to
 getting a column from a DataFrame, you can do:
 
 .. ipython:: python
-   :suppress:
 
    df = pd.DataFrame(
        {
@@ -402,7 +401,7 @@ getting a column from a DataFrame, you can do:
        }
    )
 
-.. ipython:: python
+   df
 
    grouped = df.groupby(["A"])
    grouped_C = grouped["C"]

doc/source/whatsnew/v1.4.0.rst

@@ -174,7 +174,11 @@ Bug fixes
 
 Categorical
 ^^^^^^^^^^^
--
+- Bug in setting dtype-incompatible values into a :class:`Categorical` (or ``Series`` or ``DataFrame`` backed by ``Categorical``) raising ``ValueError`` instead of ``TypeError`` (:issue:`41919`)
+- Bug in :meth:`Categorical.searchsorted` when passing a dtype-incompatible value raising ``KeyError`` instead of ``TypeError`` (:issue:`41919`)
+- Bug in :meth:`Series.where` with ``CategoricalDtype`` when passing a dtype-incompatible value raising ``ValueError`` instead of ``TypeError`` (:issue:`41919`)
+- Bug in :meth:`Categorical.fillna` when passing a dtype-incompatible value raising ``ValueError`` instead of ``TypeError`` (:issue:`41919`)
+- Bug in :meth:`Categorical.fillna` with a tuple-like category raising ``ValueError`` instead of ``TypeError`` when filling with a non-category tuple (:issue:`41919`)
 -
 
 Datetimelike
@@ -229,6 +233,7 @@ Missing
 
 MultiIndex
 ^^^^^^^^^^
+- Bug in :meth:`MultiIndex.get_loc` where the first level is a :class:`DatetimeIndex` and a string key is passed (:issue:`42465`)
 - Bug in :meth:`MultiIndex.reindex` when passing a ``level`` that corresponds to an ``ExtensionDtype`` level (:issue:`42043`)
 -
 

pandas/core/arrays/categorical.py

@@ -1394,17 +1394,14 @@ def map(self, mapper):
     # -------------------------------------------------------------
     # Validators; ideally these can be de-duplicated
 
-    def _validate_searchsorted_value(self, value):
-        # searchsorted is very performance sensitive. By converting codes
-        # to same dtype as self.codes, we get much faster performance.
-        if is_scalar(value):
-            codes = self._unbox_scalar(value)
+    def _validate_setitem_value(self, value):
+        if not is_hashable(value):
+            # wrap scalars and hashable-listlikes in list
+            return self._validate_listlike(value)
         else:
-            locs = [self.categories.get_loc(x) for x in value]
-            # error: Incompatible types in assignment (expression has type
-            # "ndarray", variable has type "int")
-            codes = np.array(locs, dtype=self.codes.dtype)  # type: ignore[assignment]
-        return codes
+            return self._validate_scalar(value)
+
+    _validate_searchsorted_value = _validate_setitem_value
 
     def _validate_scalar(self, fill_value):
         """
@@ -1430,8 +1427,8 @@ def _validate_scalar(self, fill_value):
             fill_value = self._unbox_scalar(fill_value)
         else:
             raise TypeError(
-                f"'fill_value={fill_value}' is not present "
-                "in this Categorical's categories"
+                "Cannot setitem on a Categorical with a new "
+                f"category ({fill_value}), set the categories first"
             )
         return fill_value
 
@@ -2016,37 +2013,35 @@ def __getitem__(self, key):
             deprecate_ndim_indexing(result)
         return result
 
-    def _validate_setitem_value(self, value):
+    def _validate_listlike(self, value):
+        # NB: here we assume scalar-like tuples have already been excluded
         value = extract_array(value, extract_numpy=True)
 
         # require identical categories set
         if isinstance(value, Categorical):
             if not is_dtype_equal(self.dtype, value.dtype):
-                raise ValueError(
+                raise TypeError(
                     "Cannot set a Categorical with another, "
                     "without identical categories"
                 )
             # is_dtype_equal implies categories_match_up_to_permutation
             value = self._encode_with_my_categories(value)
             return value._codes
 
-        # wrap scalars and hashable-listlikes in list
-        rvalue = value if not is_hashable(value) else [value]
-
         from pandas import Index
 
         # tupleize_cols=False for e.g. test_fillna_iterable_category GH#41914
-        to_add = Index(rvalue, tupleize_cols=False).difference(self.categories)
+        to_add = Index(value, tupleize_cols=False).difference(self.categories)
 
         # no assignments of values not in categories, but it's always ok to set
         # something to np.nan
         if len(to_add) and not isna(to_add).all():
-            raise ValueError(
+            raise TypeError(
                 "Cannot setitem on a Categorical with a new "
                 "category, set the categories first"
             )
 
-        codes = self.categories.get_indexer(rvalue)
+        codes = self.categories.get_indexer(value)
         return codes.astype(self._ndarray.dtype, copy=False)
 
     def _reverse_indexer(self) -> dict[Hashable, npt.NDArray[np.intp]]:

pandas/core/frame.py

@@ -3452,7 +3452,7 @@ def __getitem__(self, key):
         else:
             if is_iterator(key):
                 key = list(key)
-            indexer = self.loc._get_listlike_indexer(key, axis=1)[1]
+            indexer = self.columns._get_indexer_strict(key, "columns")[1]
 
         # take() does not accept boolean indexers
         if getattr(indexer, "dtype", None) == bool:

pandas/core/indexes/base.py

@@ -5384,6 +5384,89 @@ def get_indexer_for(self, target) -> npt.NDArray[np.intp]:
         indexer, _ = self.get_indexer_non_unique(target)
         return indexer
 
+    def _get_indexer_strict(self, key, axis_name: str_t) -> tuple[Index, np.ndarray]:
+        """
+        Analogue to get_indexer that raises if any elements are missing.
+        """
+        keyarr = key
+        if not isinstance(keyarr, Index):
+            keyarr = com.asarray_tuplesafe(keyarr)
+
+        if self._index_as_unique:
+            indexer = self.get_indexer_for(keyarr)
+            keyarr = self.reindex(keyarr)[0]
+        else:
+            keyarr, indexer, new_indexer = self._reindex_non_unique(keyarr)
+
+        self._raise_if_missing(keyarr, indexer, axis_name)
+
+        if (
+            needs_i8_conversion(self.dtype)
+            or is_categorical_dtype(self.dtype)
+            or is_interval_dtype(self.dtype)
+        ):
+            # For CategoricalIndex take instead of reindex to preserve dtype.
+            #  For IntervalIndex this is to map integers to the Intervals they match to.
+            keyarr = self.take(indexer)
+            if keyarr.dtype.kind in ["m", "M"]:
+                # DTI/TDI.take can infer a freq in some cases when we dont want one
+                if isinstance(key, list) or (
+                    isinstance(key, type(self))
+                    # "Index" has no attribute "freq"
+                    and key.freq is None  # type: ignore[attr-defined]
+                ):
+                    keyarr = keyarr._with_freq(None)
+
+        return keyarr, indexer
+
+    def _raise_if_missing(self, key, indexer, axis_name: str_t):
+        """
+        Check that indexer can be used to return a result.
+
+        e.g. at least one element was found,
+        unless the list of keys was actually empty.
+
+        Parameters
+        ----------
+        key : list-like
+            Targeted labels (only used to show correct error message).
+        indexer: array-like of booleans
+            Indices corresponding to the key,
+            (with -1 indicating not found).
+        axis_name : str
+
+        Raises
+        ------
+        KeyError
+            If at least one key was requested but none was found.
+        """
+        if len(key) == 0:
+            return
+
+        # Count missing values
+        missing_mask = indexer < 0
+        nmissing = missing_mask.sum()
+
+        if nmissing:
+
+            # TODO: remove special-case; this is just to keep exception
+            #  message tests from raising while debugging
+            use_interval_msg = is_interval_dtype(self.dtype) or (
+                is_categorical_dtype(self.dtype)
+                # "Index" has no attribute "categories"  [attr-defined]
+                and is_interval_dtype(
+                    self.categories.dtype  # type: ignore[attr-defined]
+                )
+            )
+
+            if nmissing == len(indexer):
+                if use_interval_msg:
+                    key = list(key)
+                raise KeyError(f"None of [{key}] are in the [{axis_name}]")
+
+            not_found = list(ensure_index(key)[missing_mask.nonzero()[0]].unique())
+            raise KeyError(f"{not_found} not in index")
+
     @overload
     def _get_indexer_non_comparable(
         self, target: Index, method, unique: Literal[True] = ...

pandas/core/indexes/multi.py

@@ -2541,24 +2541,28 @@ def _get_values_for_loc(self, series: Series, loc, key):
         new_ser = series._constructor(new_values, index=new_index, name=series.name)
         return new_ser.__finalize__(series)
 
-    def _convert_listlike_indexer(self, keyarr) -> np.ndarray | None:
-        """
-        Analogous to get_indexer when we are partial-indexing on our first level.
-
-        Parameters
-        ----------
-        keyarr : Index, np.ndarray, or ExtensionArray
-            Indexer to convert.
+    def _get_indexer_strict(self, key, axis_name: str) -> tuple[Index, np.ndarray]:
 
-        Returns
-        -------
-        np.ndarray[intp] or None
-        """
-        indexer = None
+        keyarr = key
+        if not isinstance(keyarr, Index):
+            keyarr = com.asarray_tuplesafe(keyarr)
 
-        # are we indexing a specific level
         if len(keyarr) and not isinstance(keyarr[0], tuple):
             indexer = self._get_indexer_level_0(keyarr)
+
+            self._raise_if_missing(key, indexer, axis_name)
+            return self[indexer], indexer
+
+        return super()._get_indexer_strict(key, axis_name)
+
+    def _raise_if_missing(self, key, indexer, axis_name: str):
+        keyarr = key
+        if not isinstance(key, Index):
+            keyarr = com.asarray_tuplesafe(key)
+
+        if len(keyarr) and not isinstance(keyarr[0], tuple):
+            # i.e. same condition for special case in MultiIndex._get_indexer_strict
+
             mask = indexer == -1
             if mask.any():
                 check = self.levels[0].get_indexer(keyarr)
@@ -2568,8 +2572,8 @@ def _convert_listlike_indexer(self, keyarr) -> np.ndarray | None:
                 # We get here when levels still contain values which are not
                 # actually in Index anymore
                 raise KeyError(f"{keyarr} not in index")
-
-        return indexer
+        else:
+            return super()._raise_if_missing(key, indexer, axis_name)
 
     def _get_indexer_level_0(self, target) -> np.ndarray:
         """
@@ -3160,10 +3164,12 @@ def convert_indexer(start, stop, step, indexer=indexer, codes=level_codes):
             if level > 0 or self._lexsort_depth == 0:
                 # Desired level is not sorted
                 if isinstance(idx, slice):
+                    # test_get_loc_partial_timestamp_multiindex
                     locs = (level_codes >= idx.start) & (level_codes < idx.stop)
                     return locs
 
                 locs = np.array(level_codes == idx, dtype=bool, copy=False)
+
                 if not locs.any():
                     # The label is present in self.levels[level] but unused:
                     raise KeyError(key)