A Python property decorator that can chain decorated property.

chnpropdeco.py

#!/home/verdi/miniconda3/bin/python3.6

'''
Demonstrate a property decorator that can chain decorated property.
For chaining to work, decoratee must be a plain function or a property with
fget attribute.

Sample outputs:

(py36) verdi@verdi-VirtualBox:/tmp$ ./haha.py 
########
class Test...
########
deco.__call__(fget=<function Test.x at 0xb6f0a614>)
deco.__call__(fget=<function Test.x at 0xb6f0a614>)
deco.__call__(fget=<function Test._y at 0xb6f0a5cc>)

########
class TTest(...)
########
deco.__call__(fget=<function TTest.x at 0xb6f0a584>)
deco.__call__(fget=<__main__.deco object at 0xb6f183ec>)
deco.__call__(fget=<property object at 0xb6f28824>)

########
t.x, t.y, t.x2
########
[decoratee == plain old function] deco(darg=100): name=x, <function Test.x at 0xb6f0a614>, val=10
[decoratee == plain old function] deco(darg=200): name=y, <function Test._y at 0xb6f0a5cc>, val=20
[decoratee == plain old function] deco(darg=102): name=x2, <function Test.x at 0xb6f0a614>, val=10
results: 10 20 10

########
tt.x3, tt.y2
########
[decoratee == property or deco] deco(darg=103): name=x3, <__main__.deco object at 0xb6f183ec>, recursing...
[decoratee == plain old function] deco(darg=100): name=x, <function TTest.x at 0xb6f0a584>, val=11
 => deco(darg=103): recurse ended, val=11
[decoratee == property or deco] deco(darg=200): name=y2, <property object at 0xb6f28824>, recursing...
 => deco(darg=200): recurse ended, val=21
results: 11 21
y.setter invoked
[decoratee == property or deco] deco(darg=103): name=x3, <__main__.deco object at 0xb6f183ec>, recursing...
[decoratee == plain old function] deco(darg=100): name=x, <function TTest.x at 0xb6f0a584>, val=11
 => deco(darg=103): recurse ended, val=11
[decoratee == property or deco] deco(darg=200): name=y2, <property object at 0xb6f28824>, recursing...
 => deco(darg=200): recurse ended, val=44
results: 11 44
'''
class deco(object):
    def __init__(self, darg=100):
        self.darg = darg
    def __call__(self, fget):
        print(f'deco.__call__(fget={fget})')
        self.fget = fget
        return self
    def __set_name__(self, owner, name):
        # New since Python 3.6
        self.name = name

    def __get__(self, inst, owner):
        if not hasattr(self.fget, 'fget'):
            print(f'[decoratee == plain old function] deco(darg={self.darg}): name={self.name}, {self.fget}, ', end='')
            val = self.fget(inst)
            print(f'val={val}')
        else:
            print(f'[decoratee == property or deco] deco(darg={self.darg}): name={self.name}, {self.fget}, recursing...')
            #descriptor = self.__dict__['fget']
            #val = descriptor.__get__(inst, owner)
            val = self.fget.__get__(inst, owner)
            print(f' => deco(darg={self.darg}): recurse ended, val={val}')
        return val

print('#' * 8)
print('class Test...')
print('#' * 8)
class Test(object):
    @deco()
    def x(self):
        return 10

    x2 = deco(darg=102)(x.fget)

    def _y(self):
        return 20
    y = deco(darg=200)(_y)


print('\n' + '#' * 8)
print('class TTest(...)')
print('#' * 8)

class TTest(object):
    def __init__(self):
        self._y = 21
    @deco()
    def x(self):
        return 11

    x3 = deco(darg=103)(x)

    @property
    def y(self):
        return self._y

    @y.setter
    def y(self, yy):
        print("y.setter invoked")
        self._y = yy

    y2 = deco(darg=200)(y)

if __name__ == '__main__':
    print('\n' + '#' * 8)
    print('t.x, t.y, t.x2')
    print('#' * 8)
    t = Test()
    print('results:', t.x, t.y, t.x2)

    print('\n' + '#' * 8)
    print('tt.x3, tt.y2')
    print('#' * 8)
    tt = TTest()
    print('results:', tt.x3, tt.y2)

    tt.y = 44
    print('results:', tt.x3, tt.y2)