How can I retrieve the docstring for a property of a Python class instance?

Question

Suppose I have a class like this:

class TestCase(object):
    """Class docstring"""

    def meth(self):
        """Method docstring"""
        return 1

    @property
    def prop(self):
        """Property docstring"""
        return 2

It's easy enough for me to get the docstrings for the class itself, or for a regular method:

tc = TestCase()

print(tc.__doc__)
# Class docstring

print(tc.meth.__doc__)
# Method docstring

However, this approach doesn't work for properties - instead I get the __doc__ attribute of whatever object is returned by the property getter method (in this case, int):

print(tc.prop.__doc__)
# int(x=0) -> int or long
# int(x, base=10) -> int or long
# ...

The same thing applies to getattr(tc, "prop").__doc__ and getattr(tc.prop, "__doc__").

I know that Python's introspection mechanisms are capable of accessing the docstring I'm looking for. For example, when I call help(tc) I get:

class TestCase(__builtin__.object)
 |  Class docstring
 |  
 |  Methods defined here:
 |  
 |  meth(self)
 |      Method docstring
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  __dict__
 |      dictionary for instance variables (if defined)
 |  
 |  __weakref__
 |      list of weak references to the object (if defined)
 |  
 |  prop
 |      Property docstring

How is help able to access the docstring for tc.prop?

Answer 1

You are trying to access the __doc__ from the instance which will try to first , evaluate the property, for which the returned value may have no attribute __doc__, or use the __doc__ of the returned type.

Instead, you should access the __doc__ for the property from the class itself:

TestCase.prop.__doc__

So to extend this to your class instance, you would use __class__ to get the class of the instance and then the property, and finally the __doc__:

tc.__class__.prop.__doc__

Or use type to fetch the class:

type(tc).prop.__doc__