Question

I have a Class, it will be implemented to be many instances. I want to keep connections between some of the instances, and pass messages among them. In C++, I can do this like:

class A
{
   A (*connections)[];
   int sum;

public:
   void pass(int index)
   {
       connections[index] -> receive(sum);
   }
   void receive(int input)
   {
       sum += input;
   }
}

Then I only need to add pointers of other instances to connections[], I can pass messages among them with each other.

Currently I have to use Python doing this, but Python doesn’t support pointers. I wonder what is the proper solution, or design pattern, to solve this problem?

Thank you in advance.

Answer 1

Python doesn’t need pointers in order to achieve this as every variable is a reference to an object. These references are slightly different from C++ references, in that they can be assigned to – much like pointers in C++.

So to achieve what you’re looking for, you’d just need to do something like this:

class A(object):
    def __init__( self, connections, sum ):
        self.connections = connections
        self.sum = sum

    def passToConnections( self, index ):
        self.connections[ index ].receive( self.sum )

    def receive( self, input ):
       self.sum += input

And just to prove that this works as expected:

>>> a1 = A( [], 0 )
>>> a2 = A( [], 0 )
>>> a3 = A( [ a1, a2 ], 10 )
>>> a3.passToConnections( 0 )
>>> a3.passToConnections( 1 )
>>> a3.passToConnections( 1 )
>>> print a1.sum
10
>>> print a2.sum
20

So as you can see we have altered the original objects a1 and a2 by calling through to them via the references in a3