BUG: NumericIndex.astype(complex) should return Index[complex] (pandas-dev#49540)

Co-authored-by: Terji Petersen <[email protected]>

Author: 2 people

pandas/conftest.py

@@ -597,8 +597,8 @@ def _create_mi_with_dt64tz_level():
     "uint": tm.makeUIntIndex(100),
     "range": tm.makeRangeIndex(100),
     "float": tm.makeFloatIndex(100),
-    "complex64": tm.makeFloatIndex(100).astype("complex64"),
-    "complex128": tm.makeFloatIndex(100).astype("complex128"),
+    "complex64": tm.makeNumericIndex(100, dtype="float64").astype("complex64"),
+    "complex128": tm.makeNumericIndex(100, dtype="float64").astype("complex128"),
     "num_int64": tm.makeNumericIndex(100, dtype="int64"),
     "num_int32": tm.makeNumericIndex(100, dtype="int32"),
     "num_int16": tm.makeNumericIndex(100, dtype="int16"),

pandas/core/indexes/base.py

@@ -89,6 +89,7 @@
     ensure_platform_int,
     is_bool_dtype,
     is_categorical_dtype,
+    is_complex_dtype,
     is_dtype_equal,
     is_ea_or_datetimelike_dtype,
     is_extension_array_dtype,
@@ -1044,7 +1045,11 @@ def astype(self, dtype, copy: bool = True):
             # this block is needed so e.g. NumericIndex[int8].astype("int32") returns
             # NumericIndex[int32] and not Int64Index with dtype int64.
             # When Int64Index etc. are removed from the code base, removed this also.
-            if isinstance(dtype, np.dtype) and is_numeric_dtype(dtype):
+            if (
+                isinstance(dtype, np.dtype)
+                and is_numeric_dtype(dtype)
+                and not is_complex_dtype(dtype)
+            ):
                 return self._constructor(
                     new_values, name=self.name, dtype=dtype, copy=False
                 )

pandas/tests/indexes/common.py

@@ -896,3 +896,9 @@ def test_invalid_dtype(self, invalid_dtype):
         msg = rf"Incorrect `dtype` passed: expected \w+(?: \w+)?, received {dtype}"
         with pytest.raises(ValueError, match=msg):
             self._index_cls([1, 2, 3], dtype=dtype)
+
+    @pytest.mark.parametrize("complex_dtype", [np.complex64, np.complex128])
+    def test_astype_to_complex(self, complex_dtype, simple_index):
+        result = simple_index.astype(complex_dtype)
+
+        assert type(result) is Index and result.dtype == complex_dtype