检查类属性是否有 setter

Question

I need to list all the attribute of a class that are properties and have a setter. For example with this class:

class MyClass(object):
    def __init__(self):
        self. a = 1
        self._b = 2
        self._c = 3

    @property
    def b(self):
        return self._b

    @property
    def c(self):
        return self._c

    @c.setter
    def c(self, value):
        self._c = value

I need to get the attribute c but not a and b. Using this answers: https://stackoverflow.com/a/5876258/7529716 i can get the property object b and c.

But is their a way to know if those properties have a setter other than trying:

inst = MyClass()    
try:
    prev = inst.b
    inst.b = None
except AttributeError:
    pass # No setter
finally:
    inst.b = prev  

Thanks in advance.

Answer 1

property objects store their getter, setter and deleter in the fget , fset and fdel attributes, respectively. If a property doesn't have a setter or deleter, the attribute is set to None .

This means you can simply filter out those properties whose fset attribute is set to None :

def get_writeable_properties(cls):
    return [attr for attr, value in vars(cls).items()
                 if isinstance(value, property) and value.fset is not None]

>>> get_writeable_properties(MyClass)
['c']