BUG: Fix __instancecheck__ and __subclasscheck__ of metaclass in pandas.core.dtypes.generic (pandas-dev#46719)

Author: leonarduschen

doc/source/whatsnew/v1.5.0.rst

@@ -499,6 +499,7 @@ Conversion
 - Bug in :meth:`Series.astype` and :meth:`DataFrame.astype` from floating dtype to unsigned integer dtype failing to raise in the presence of negative values (:issue:`45151`)
 - Bug in :func:`array` with ``FloatingDtype`` and values containing float-castable strings incorrectly raising (:issue:`45424`)
 - Bug when comparing string and datetime64ns objects causing ``OverflowError`` exception. (:issue:`45506`)
+- Bug in metaclass of generic abstract dtypes causing :meth:`DataFrame.apply` and :meth:`Series.apply` to raise for the built-in function ``type`` (:issue:`46684`)
 
 Strings
 ^^^^^^^

pandas/core/dtypes/generic.py

@@ -37,14 +37,25 @@
 # define abstract base classes to enable isinstance type checking on our
 # objects
 def create_pandas_abc_type(name, attr, comp):
+    def _check(inst):
+        return getattr(inst, attr, "_typ") in comp
 
     # https://github.com/python/mypy/issues/1006
     # error: 'classmethod' used with a non-method
     @classmethod  # type: ignore[misc]
-    def _check(cls, inst) -> bool:
-        return getattr(inst, attr, "_typ") in comp
+    def _instancecheck(cls, inst) -> bool:
+        return _check(inst) and not isinstance(inst, type)
+
+    @classmethod  # type: ignore[misc]
+    def _subclasscheck(cls, inst) -> bool:
+        # Raise instead of returning False
+        # This is consistent with default __subclasscheck__ behavior
+        if not isinstance(inst, type):
+            raise TypeError("issubclass() arg 1 must be a class")
+
+        return _check(inst)
 
-    dct = {"__instancecheck__": _check, "__subclasscheck__": _check}
+    dct = {"__instancecheck__": _instancecheck, "__subclasscheck__": _subclasscheck}
     meta = type("ABCBase", (type,), dct)
     return meta(name, (), dct)
 

pandas/tests/apply/test_frame_apply.py

@@ -1551,3 +1551,29 @@ def foo(x):
     df = DataFrame({"a": [1, 2, 3]})
     with tm.assert_produces_warning(UserWarning, match="Hello, World!"):
         df.agg([foo])
+
+
+def test_apply_type():
+    # GH 46719
+    df = DataFrame(
+        {"col1": [3, "string", float], "col2": [0.25, datetime(2020, 1, 1), np.nan]},
+        index=["a", "b", "c"],
+    )
+
+    # applymap
+    result = df.applymap(type)
+    expected = DataFrame(
+        {"col1": [int, str, type], "col2": [float, datetime, float]},
+        index=["a", "b", "c"],
+    )
+    tm.assert_frame_equal(result, expected)
+
+    # axis=0
+    result = df.apply(type, axis=0)
+    expected = Series({"col1": Series, "col2": Series})
+    tm.assert_series_equal(result, expected)
+
+    # axis=1
+    result = df.apply(type, axis=1)
+    expected = Series({"a": Series, "b": Series, "c": Series})
+    tm.assert_series_equal(result, expected)

pandas/tests/apply/test_series_apply.py

@@ -889,3 +889,11 @@ def test_apply_retains_column_name():
         index=Index(range(3), name="x"),
     )
     tm.assert_frame_equal(result, expected)
+
+
+def test_apply_type():
+    # GH 46719
+    s = Series([3, "string", float], index=["a", "b", "c"])
+    result = s.apply(type)
+    expected = Series([int, str, type], index=["a", "b", "c"])
+    tm.assert_series_equal(result, expected)

pandas/tests/dtypes/test_generic.py

@@ -1,3 +1,4 @@
+import re
 from warnings import catch_warnings
 
 import numpy as np
@@ -49,13 +50,28 @@ class TestABCClasses:
 
     @pytest.mark.parametrize("abctype1, inst", abc_pairs)
     @pytest.mark.parametrize("abctype2, _", abc_pairs)
-    def test_abc_pairs(self, abctype1, abctype2, inst, _):
-        # GH 38588
+    def test_abc_pairs_instance_check(self, abctype1, abctype2, inst, _):
+        # GH 38588, 46719
         if abctype1 == abctype2:
             assert isinstance(inst, getattr(gt, abctype2))
+            assert not isinstance(type(inst), getattr(gt, abctype2))
         else:
             assert not isinstance(inst, getattr(gt, abctype2))
 
+    @pytest.mark.parametrize("abctype1, inst", abc_pairs)
+    @pytest.mark.parametrize("abctype2, _", abc_pairs)
+    def test_abc_pairs_subclass_check(self, abctype1, abctype2, inst, _):
+        # GH 38588, 46719
+        if abctype1 == abctype2:
+            assert issubclass(type(inst), getattr(gt, abctype2))
+
+            with pytest.raises(
+                TypeError, match=re.escape("issubclass() arg 1 must be a class")
+            ):
+                issubclass(inst, getattr(gt, abctype2))
+        else:
+            assert not issubclass(type(inst), getattr(gt, abctype2))
+
     abc_subclasses = {
         "ABCIndex": [
             abctype