added tests

Author: debnathshoham

pandas/core/frame.py

@@ -4281,7 +4281,10 @@ def check_int_infer_dtype(dtypes):
                     # "Type[signedinteger[Any]]"; expected "Type[signedinteger[Any]]"
                     converted_dtypes.append(np.int64)  # type: ignore[arg-type]
                 elif dtype == "float":
-                    converted_dtypes.extend([np.float64, np.float32])
+                    # GH#42452 : np.dtype("float") coerces to np.float64 from Numpy 1.20
+                    converted_dtypes.extend(
+                        [np.float64, np.float32, np.float16]
+                    )  # type: ignore[list-item]
                 else:
                     # error: Argument 1 to "append" of "list" has incompatible type
                     # "Union[dtype[Any], ExtensionDtype]"; expected

pandas/tests/window/test_ewm.py

@@ -181,3 +181,14 @@ def test_ewma_times_adjust_false_raises():
         Series(range(1)).ewm(
             0.1, adjust=False, times=date_range("2000", freq="D", periods=1)
         )
+
+
+@pytest.mark.parametrize("func", ["mean", "std", "var"])
+@pytest.mark.parametrize("dtype", [np.float32, np.float16, np.float64, float, "float"])
+def test_float_dtype_ewma(dtype, func):
+    # GH#42452
+    df = DataFrame(np.random.rand(20, 3), dtype=dtype)
+    e = df.ewm(alpha=0.5, axis=1)
+    result = getattr(e, func)().shape
+    expected = (20, 3)
+    assert result == expected, f"Shape of ewm {func} must match dataframe"