How to use the docstring in this property example

[Steven D'Aprano]

On Thursday 21 January 2016 15:00, Robert wrote:

> Hi,
> 
> I read below code snippet on link:
> https://docs.python.org/2/library/functions.html#property

Property docstrings are hard to get to. But with the class C you gave, this 
works in the interactive interpreter:

help(C.__dict__['x'])

displays:

    I'm the 'x' property.


C.__dict__['x'] will return the property object itself, without running the 
getter or setter, so you can access the dostring:


py> C.__dict__['x']
<property object at 0xb7171d9c>
py> C.__dict__['x'].__doc__
"I'm the 'x' property."



But what happens if you inherit the property from some other class?

py> class D(C): pass
... 
py> class E(D): pass
... 
py> E.__dict__['x']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'x'



In Python 3, you can use the inspect module:

py> obj = inspect.getattr_static(E, 'x')
py> inspect.getdoc(obj)
"I'm the 'x' property."



but in Python 2, you may need to walk the class's MRO by hand. Something 
like this:


def getattr_static(obj, name):
    if isinstance(obj, type):
        for cls in obj.__mro__:
            if name in cls.__dict__:
                return cls.__dict__[name]


-- 
Steve