Automatically fill a list in a class when I add a method in a subclass

Question

Here is the context simplified:

class A(object):
    def __init__(self):
        self.vocab = [
            ('method1', self.method1),
            ('method2', 'arg2', self.method2),
            ('method3', self.method3),
        ]

class SubA(A):
    def method4(self):
        pass
    def method5(self, arg5):
        pass

class SubB(A):
    def method6(self):
        pass
    def method7(self):
        pass

I want to "automatically" fill self.vocab list from class A with all method from all subclasses and following the rule defined in self.vocab initialisation. So in this example I want to add method4,...,method7 automatically when object is instanciate. So self.vocab becomes:

    self.vocab = [
        ('method4', self.method4),
        ('method5', 'arg5', self.method5),
        ('method6', self.method6),
        ('method7', self.method7),
        ('method1', self.method1),
        ('method2', 'arg2', self.method2),
        ('method3', self.method3),
    ]

I think I have to change A into metaclass and use __new__ instead because I think it must be done before instanciation. In fact the class A is introspected by another code. self.vocab is extracted during instantiation and that's why I think it must be done before.

I don't know how to proceed and if it's possible.

score 3 · Accepted Answer · edited May 23 '17 at 12:05

3

The inspect module contains all tools that you need for this.

See this question how to get all methods of a class: How do I get list of methods in a Python class?

You can get your own current class in __init__ using self.__class__.

edited May 23 '17 at 12:05

Community

1
1

answered Nov 14 '13 at 15:38

Aaron Digulla

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+1 for inspect module. I will see more in details and I come back. – Katsu Nov 14 '13 at 16:14
You finally anwers the question (`self.__class__` in init). But in fact the inspection must be done after import of module (classes) and before instanciation. But it's another question I will post later. – Katsu Nov 14 '13 at 17:22

score 1 · Answer 2 · answered Nov 14 '13 at 16:15

1

So, here is my solution. I changed initial setup a bit, though I tried to keep the original idea:

import inspect


class A(object):

    vocab = set()

    def __new__(cls, *args, **kwargs):
        A.vocab.update(inspect.getmembers(cls, inspect.ismethod))


class SubA(A):

    def method4(self):
        pass

    def method5(self, arg5):
        pass


class SubB(A):

    def method6(self):
        pass

    def method7(self):
        pass


print A.vocab  # set([])
SubA()
SubA()
SubB()
print A.vocab # set([('method5', <unbound method SubA.method5>), ('method6', <unbound method SubB.method6>), ('method4', <unbound method SubA.method4>), ('method7', <unbound method SubB.method7>)])

answered Nov 14 '13 at 16:15

Alexander Zhukov

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It seems to work when I try with dummy class. But here my classes are introspected by another code and if I add `__new__` method, it returns the error:`AttributeError: 'NoneType' object has no attribute 'vocab'`. Maybe I have to return something in new method? Of course I added the __init__ method with all features. – Katsu Nov 14 '13 at 17:02
In fact I have to had in __new__ method at the end: `return super(A, cls).__new__(cls)`. But it is the same as to do it before initialisation and with self.__class__ as reference (see @Aaron Digulla) – Katsu Nov 14 '13 at 17:17

score 0 · Answer 3 · edited Jan 05 '14 at 16:08

0

Actually inspect package can do every thing for you. you can use it like this..

inspect.getmembers(mod, inspect.isfunction) # returns all the members of the given module which are functions

But you can change the predicate such as isfunction, isclass, ismethod for bound methods etc.

Hope this helps :)

edited Jan 05 '14 at 16:08

BenMorel

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answered Nov 14 '13 at 15:44

Sravan K Ghantasala

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Automatically fill a list in a class when I add a method in a subclass

3 Answers3