BUG: support dtypes in column_dtypes for to_records()

Author: qwhelan

pandas/core/frame.py

@@ -1716,7 +1716,8 @@ def to_records(self, index=True, convert_datetime64=None,
             # string naming a type.
             if dtype_mapping is None:
                 formats.append(v.dtype)
-            elif isinstance(dtype_mapping, (type, compat.string_types)):
+            elif isinstance(dtype_mapping, (type, np.dtype,
+                                            compat.string_types)):
                 formats.append(dtype_mapping)
             else:
                 element = "row" if i < index_len else "column"

pandas/tests/frame/test_convert_to.py

@@ -274,6 +274,29 @@ def test_to_records_dtype(self, kwargs, expected):
             result = df.to_records(**kwargs)
             tm.assert_almost_equal(result, expected)
 
+    @pytest.mark.parametrize("kwargs,expected", [
+        # Pass in a dtype instance.
+        (dict(column_dtypes=np.dtype('unicode')),
+         np.rec.array([("0", "1", "0.2", "a"), ("1", "2", "1.5", "bc")],
+                      dtype=[("index", "<i8"), ("A", "<U"),
+                             ("B", "<U"), ("C", "<U")])),
+
+        # Names / indices not in mapping default to array dtype.
+        (dict(column_dtypes={"A": np.dtype('int8'), "B": np.dtype('float32')}),
+         np.rec.array([("0", "1", "0.2", "a"), ("1", "2", "1.5", "bc")],
+                      dtype=[("index", "<i8"), ("A", "i1"),
+                             ("B", "<f4"), ("C", "O")]))])
+    def test_to_records_dtype_dtype(self, kwargs, expected):
+        # See gh-24895
+        df = DataFrame({"A": [1, 2], "B": [0.2, 1.5], "C": ["a", "bc"]})
+
+        if isinstance(expected, str):
+            with pytest.raises(ValueError, match=expected):
+                df.to_records(**kwargs)
+        else:
+            result = df.to_records(**kwargs)
+            tm.assert_almost_equal(result, expected)
+
     @pytest.mark.parametrize("df,kwargs,expected", [
         # MultiIndex in the index.
         (DataFrame([[1, 2, 3], [4, 5, 6], [7, 8, 9]],