从对象列表中获取价值

Question

I try to write a program which will generate me all possible combinations of positions in given range of X and Y. For example: [A1,A2,A3,B1,...] As I am new to OOP I have some problem with printing these values. Below is my code:

X = ['A','B','C']  
Y = ['1','2','3']

class Combination:
    def __init__(self,x,y):
        if (x in X) and (y in Y):
            self.x = x
            self.y = y
        else:
            print "WRONG!!"

    def __str__ (self):
        return x+y

class Position:
    def __init__(self):
        self.xy = []
        for i in X:
            for j in Y:
                self.xy.append(Combination(i,j))
    def __str__(self):
        return "List contains: " + str(self.xy)

P1 = Position()
print P1

My result is:

List contains: [<__main__.Combination object>, <__main__.Combination object>,....

As I mentioned, I would like to see something like that: [A1,A2,A3,B1,...] If I change line:

 self.xy.append(Combination(i,j))

to:

 self.xy.append(i,j)

It works fine but I want to use class Combination there.

Does anyone know how to do it? What is wrong here?

Answer 1

In the Combinations class, you need to define __repr__ method, instead of __str__ like this

def __repr__ (self):
    return self.x+self.y

with this change, the output is

List contains: [A1, A2, A3, B1, B2, B3, C1, C2, C3]

Answer 2

Your Combination __str__ method needs improving. Firstly, I suspect it should be __repr__ and secondly it needs self.x + self.y