BUG: Raise TypeError for mismatched signed/unsigned dtypes in IntervalIndex.from_arrays

doc/source/whatsnew/v3.0.0.rst

@@ -958,7 +958,7 @@ Interval
 ^^^^^^^^
 - :meth:`Index.is_monotonic_decreasing`, :meth:`Index.is_monotonic_increasing`, and :meth:`Index.is_unique` could incorrectly be ``False`` for an ``Index`` created from a slice of another ``Index``. (:issue:`57911`)
 - Bug in :func:`interval_range` where start and end numeric types were always cast to 64 bit (:issue:`57268`)
--
+- Construction of :class:`IntervalArray` and :class:`IntervalIndex` from arrays with mismatched signed/unsigned integer dtypes (e.g., ``int64`` and ``uint64``) now raises a :exc:`TypeError` instead of proceeding silently. (:issue:`55715`)
 
 Indexing
 ^^^^^^^^

pandas/core/arrays/interval.py

@@ -263,6 +263,19 @@ def __new__(
                 dtype=dtype,
             )
 
+            # Check for mismatched signed/unsigned integer dtypes after casting
+            left_dtype = left.dtype
+            right_dtype = right.dtype
+            if (
+                left_dtype.kind in "iu"
+                and right_dtype.kind in "iu"
+                and left_dtype.kind != right_dtype.kind
+            ):
+                raise TypeError(
+                    f"Left and right arrays must have matching signedness. "
+                    f"Got {left_dtype} and {right_dtype}."
+                )
+
         if verify_integrity:
             cls._validate(left, right, dtype=dtype)
 

pandas/io/excel/_xlsxwriter.py

@@ -213,7 +213,7 @@ def __init__(  # pyright: ignore[reportInconsistentConstructor]
         )
 
         try:
-            self._book = Workbook(self._handles.handle, **engine_kwargs)  # type: ignore[arg-type]
+            self._book = Workbook(self._handles.handle, **engine_kwargs)
         except TypeError:
             self._handles.handle.close()
             raise

pandas/tests/indexes/interval/test_interval.py

@@ -882,6 +882,14 @@ def test_is_all_dates(self):
         assert not year_2017_index._is_all_dates
 
 
+def test_from_arrays_mismatched_signedness_raises():
+    # GH 55715
+    left = np.array([0, 1, 2], dtype="int64")
+    right = np.array([1, 2, 3], dtype="uint64")
+    with pytest.raises(TypeError, match="matching signedness"):
+        IntervalIndex.from_arrays(left, right)
+
+
 def test_dir():
     # GH#27571 dir(interval_index) should not raise
     index = IntervalIndex.from_arrays([0, 1], [1, 2])