simple class question

[C GIllespie]

Dear all,

I'm new to both python and OOP, so could I ask a simple question.

I have class:

class species:
    __init__(self,pop=0):
        self.pop=pop

Now I want to do something like this:

X=species(pop=10)
Y=species(pop=X.pop)
OK, but now I want to update X.pop and have that mirrored in Y.pop, i.e. if
X.pop=5, Y.pop now equals 5.

What is the best/nicest/simplest way of doing this?

Many thanks

Colin