Access to the methods of the class from which it was instantiated another class

Question

I'm trying to access the methods of the class from which it was instantiated another class, I mean, accessing to the "parent" instance without creating a new instance of it.

class A():  
    def __init__(self):
        ...  
        b_instance = B()  
        ...

class B():
    def __init__(self):  
        ...     
    def function1(self):  
        ...  
    def function2(self):  
        C().run() # I need to use class C functionalities
        ...  

class C():  
    def __init__(self):  
        ...  
    def run(self):  
        classB.function1() #I can't access to these methods without instantiating again class B  


# I have to execute:
>>> a = A()
>>> a.b_instance.function2()

Sorry if I have not explained well, is a bit confusing. If you need any clarification do not hesitate to ask.

EDIT.

In class C a specific handling of the execution of class B methods is done. Is not possible to instanciate again inside C because class B contains the initialization of hardware.

`b_instance` is local to `A.__init__` - it won't be created until you create an instance of `A`, and will not be available outside that method (unless you make it e.g. an instance attribute). Why don't the (presumably) instance methods in `B` and `C` have the `self` parameter? Why does `C.run()` require access to a `B` instance (and, in that case, why isn't one created *in `C.__init__`*)? Could you provide a fuller example that demonstrates what you are trying to achieve in less abstract terms? — jonrsharpe, Oct 16 '14 at 10:09
Sorry I forgot to put _self_ parameter. Class C requires access to B because it makes specific handling of B methods in threads. I want to maintain isolated in other class for reutilizing from another modules. — kmsdev, Oct 16 '14 at 12:24

Vishnu Upadhyay · Answer 1 · 2014-10-16T10:30:06.813

This can access the class methods from other classes. use instance method, class methods and static methods, if you are using various types of functins.

class A():  
    def __init__(self):
        print 'in __init__'
        self.b_instance = B() # making an instance of class  
        #self.b_instance.function2()

class B():
    def __init__(self):  
        print 'in __init__, B'
    @staticmethod
    def function1():  
        print 'func1'

    def function2(self):  
        C().run() # I need to use class C functionalities

         # if you trying to access `run` method of `class C` make
          # it instance bound method"""

class C():  
    def __init__(self):  
        pass    
    def run(self):
        print 'in run'
        B.function1() #I can't access to these methods without instantiating again class B  
      #you are passing class instance as `B` while calling function1
       # so make it either classmethod `@classmethod` or `static method`

# I have to execute:
a = A()
a.b_instance.function2() # calling b_instance variable of class A

Not work for me because when I define a @staticmethod I have problems to use this method with the class itself — kmsdev, Oct 16 '14 at 13:18
I lost the access to class variables. Besides I have too many functions and I would need more time to adjust the program than with the solution suggested by jonrsharpe. Thanks anyway for the solution, I sure will be useful sometimes. — kmsdev, Oct 16 '14 at 14:02

score 0 · Accepted Answer · answered Oct 16 '14 at 11:21

0

It's still not clear what exactly you're trying to achieve, but here's one fix:

class A():  
    def __init__(self):
        ...  
        b_instance = B()  
        ...

class B():
    def __init__(self):  
        ...     
    def function1(self):  
        ...  
    def function2(self):  
        C().run(self) # pass class B instance to C instance run method
        ...  

class C():  
    def __init__(self):  
        ...  
    def run(self, classB): # note additional parameter
        classB.function1()

However, note that this represents a very high level of coupling between your various classes, which seems suspicious to me and may indicate a deeper flaw in your design.

answered Oct 16 '14 at 11:21

jonrsharpe

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This works for me! I thought to solve this would have to do very complicated things... and I forgot the most simple and intuitive way. Just a comment on your solution, I have to put additional parameter in __init__ method also: `def __init__(self, classB) – kmsdev Oct 16 '14 at 13:10
Yes, `C(self).run()` works just as well if that's preferable. – jonrsharpe Oct 16 '14 at 13:10

Access to the methods of the class from which it was instantiated another class

2 Answers2