Improved error message for invalid construction (#35190)

Author: Lewiscowles1986

doc/source/whatsnew/v1.1.0.rst

@@ -1170,6 +1170,7 @@ Other
 - Bug in :class:`Tick` comparisons raising ``TypeError`` when comparing against timedelta-like objects (:issue:`34088`)
 - Bug in :class:`Tick` multiplication raising ``TypeError`` when multiplying by a float (:issue:`34486`)
 - Passing a `set` as `names` argument to :func:`pandas.read_csv`, :func:`pandas.read_table`, or :func:`pandas.read_fwf` will raise ``ValueError: Names should be an ordered collection.`` (:issue:`34946`)
+- Improved error message for invalid construction of list when creating a new index (:issue:`35190`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/internals/construction.py

@@ -744,7 +744,12 @@ def sanitize_index(data, index: Index):
     through a non-Index.
     """
     if len(data) != len(index):
-        raise ValueError("Length of values does not match length of index")
+        raise ValueError(
+            "Length of values "
+            f"({len(data)}) "
+            "does not match length of index "
+            f"({len(index)})"
+        )
 
     if isinstance(data, np.ndarray):
 

pandas/tests/extension/base/setitem.py

@@ -244,7 +244,10 @@ def test_setitem_expand_with_extension(self, data):
 
     def test_setitem_frame_invalid_length(self, data):
         df = pd.DataFrame({"A": [1] * len(data)})
-        xpr = "Length of values does not match length of index"
+        xpr = (
+            rf"Length of values \({len(data[:5])}\) "
+            rf"does not match length of index \({len(df)}\)"
+        )
         with pytest.raises(ValueError, match=xpr):
             df["B"] = data[:5]
 

pandas/tests/frame/indexing/test_indexing.py

@@ -160,10 +160,13 @@ def test_setitem_list(self, float_frame):
         msg = "Columns must be same length as key"
         with pytest.raises(ValueError, match=msg):
             data[["A"]] = float_frame[["A", "B"]]
-
-        msg = "Length of values does not match length of index"
+        newcolumndata = range(len(data.index) - 1)
+        msg = (
+            rf"Length of values \({len(newcolumndata)}\) "
+            rf"does not match length of index \({len(data)}\)"
+        )
         with pytest.raises(ValueError, match=msg):
-            data["A"] = range(len(data.index) - 1)
+            data["A"] = newcolumndata
 
         df = DataFrame(0, index=range(3), columns=["tt1", "tt2"], dtype=np.int_)
         df.loc[1, ["tt1", "tt2"]] = [1, 2]

pandas/tests/frame/indexing/test_setitem.py

@@ -117,7 +117,10 @@ def test_setitem_wrong_length_categorical_dtype_raises(self):
         cat = Categorical.from_codes([0, 1, 1, 0, 1, 2], ["a", "b", "c"])
         df = DataFrame(range(10), columns=["bar"])
 
-        msg = "Length of values does not match length of index"
+        msg = (
+            rf"Length of values \({len(cat)}\) "
+            rf"does not match length of index \({len(df)}\)"
+        )
         with pytest.raises(ValueError, match=msg):
             df["foo"] = cat