[Python] Python @classmethod and @staticmethod decorators cause isinstance(…, FunctionType) to...

I am writing a Python metaclass that creates a special index of class members that meet certain criteria, one criterion being that those members should not be functions. I am checking this criterion with a call to isinstance for types.FunctionType:

import types

class MyMeta(type):
def __new__(cls, clsname, bases, clsdict):
field_names = [
name for name, value in clsdict.items()
# ...other conditions...
and not isinstance(value, types.FunctionType)
]
# ...


This correctly omits most methods. However, I have discovered that this does not work for any methods with @classmethod or @staticmethod decorators, and isinstance(..., types.FunctionType) is always False for such methods:

import types

class MyMeta(type):
def __new__(cls, clsname, bases, clsdict):
print(clsname)
for name, value in clsdict.items():
print(f" {name} : {repr(value)}")
print(f" FunctionType: {isinstance(value, types.FunctionType)}")
print(f" classmethod: {isinstance(value, classmethod)}")
print(f" staticmethod: {isinstance(value, staticmethod)}")
print()

# ...

class MetaTest(metaclass=MyMeta):
def normal_method(self):
pass

@classmethod
def class_method(self):
pass

@staticmethod
def static_method(self):
pass


class Test:
def normal_method(self):
pass

@classmethod
def class_method(self):
pass

@staticmethod
def static_method(self):
pass

print(Test.__name__)
for name, value in Test.__dict__.items():
print(f" {name} : {repr(value)}")
print(f" FunctionType: {isinstance(value, types.FunctionType)}")
print(f" classmethod: {isinstance(value, classmethod)}")
print(f" staticmethod: {isinstance(value, staticmethod)}")
print()


The above test code produces the following output:

MetaTest
__module__ : '__main__'
FunctionType: False
classmethod: False
staticmethod: False
__qualname__ : 'TestMeta'
FunctionType: False
classmethod: False
staticmethod: False
normal_method : <function TestMeta.normal_method at 0x7fbdbc47b760>
FunctionType: True
classmethod: False
staticmethod: False
class_method : <classmethod(<function TestMeta.class_method at 0x7fbdbc47b7f0>)>
FunctionType: False
classmethod: True
staticmethod: False
static_method : <staticmethod(<function TestMeta.static_method at 0x7fbdbc47b880>)>
FunctionType: False
classmethod: False
staticmethod: True

Test
__module__ : '__main__'
FunctionType: False
classmethod: False
staticmethod: False
normal_method : <function Test.normal_method at 0x7fbdbc47b910>
FunctionType: True
classmethod: False
staticmethod: False
class_method : <classmethod(<function Test.class_method at 0x7fbdbc47b9a0>)>
FunctionType: False
classmethod: True
staticmethod: False
static_method : <staticmethod(<function Test.static_method at 0x7fbdbc47ba30>)>
FunctionType: False
classmethod: False
staticmethod: True
__dict__ : <attribute '__dict__' of 'Test' objects>
FunctionType: False
classmethod: False
staticmethod: False
__weakref__ : <attribute '__weakref__' of 'Test' objects>
FunctionType: False
classmethod: False
staticmethod: False
__doc__ : None
FunctionType: False
classmethod: False
staticmethod: False


isinstance(..., classmethod) and isinstance(..., staticmethod) both behave as expected, so one option is to replace

and not isinstance(value, types.FunctionType)


with

and not isinstance(value (types.FunctionType, classmethod, staticmethod))


which I have tested and verified that it does work. However, I find this kludgy and unmaintainable (am I supposed to exhaustively list every possible built-in decorator from now unto forever?). What I would like to know:

1. Why are methods decorated with @classmethod and @staticmethod not considered children of types.FunctionType?
2. Is there a clean way to check for functions, including methods decorated with @classmethod and @staticmethod, without exhaustively checking the return types of such decorators?

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