Question

I’m writing some serialization/deserialization code in Python that will read/write an inheritance hierarchy from some JSON. The exact composition will not be known until the request is sent in.

So, I deem the elegant solution to recursively introspect the Python class hierarchy to be emitted and then, on the way back up through the tree, install the correct values in a Python basic type.

E.g.,

A
|
|\
| \
B  C

If I call my “introspect” routine on B, it should return a dict that contains a mapping from all of A’s variables to their values, as well as B’s variables and their values.

As it now stands, I can look through B.__slots__ or B.__dict__, but I only can pull out B’s variable names from there.

How do I get the __slots__/__dict__ of A, given only B? (or C).

I know that python doesn’t directly support casting like C++ & its descendants do-

Answer 1

You might try using the type.mro() method to find the method resolution order.

class A(object):
        pass

class B(A):
        pass

class C(A):
        pass

a = A()
b = B()
c = C()

>>> type.mro(type(b))
[<class '__main__.B'>, <class '__main__.A'>, <type 'object'>]
>>> type.mro(type(c))
[<class '__main__.C'>, <class '__main__.A'>, <type 'object'>]

or

>>> type(b).mro()

---

Edit: I was thinking you wanted to do something like this…

>>> A = type("A", (object,), {'a':'A var'})  # create class A
>>> B = type("B", (A,), {'b':'B var'})       # create class B
>>> myvar = B()

def getvars(obj):
    ''' return dict where key/value is attribute-name/class-name '''
    retval = dict()
    for i in type(obj).mro():
        for k in i.__dict__:
            if not k.startswith('_'):
                retval[k] = i.__name__
    return retval

>>> getvars(myvar)
{'a': 'A', 'b': 'B'}

>>> for i in getvars(myvar):
    print getattr(myvar, i)   # or use setattr to modify the attribute value

A Var
B Var