Objects argument return value obscure

[keltik]

Hi there,
at university i have to program OO-style in Python. What i got now is a "Point"-class and a "Triangle"-class. The "Triangle"-class has a method a() that needs to return the length of the AB-edge, but it doesn't instead it concatenates the Point.__str__() methods return values together, which is exactly what i dont want. It should instead add A.self.x, A.self.y to B.self.x, B.self.y, but this is syntactically incorrect in Python. TestDrive looks like this:

class Point(object):
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y

    def __str__(self):
        return "(" + str(self.x)+ ", " + str(self.y) + ")"
        

    def __add__(self, other):
        total_x = other.x + self.x
        total_y = other.y + self.y
        return total_x, total_y


class Triangle(object):

    def __init__(self, A=Point(), B=Point(), C=Point()):
        self.A = A
        self.B = B
        self.C = C

    #omitted Triangle.__str__

    def a(self):
        A = self.A
        B = self.B
        a_b_length = A.__add__(B)
        return a_b_length        


def main():
    point_one = Point(3,5)
    point_two = Point(7,11)
    point_three = Point(6,13)
    print("A ---> "+str(point_one))
    print("B ---> "+str(point_two))
    print("__add__ ---> "+str(point_one.__add__(point_two)))
    print("__sub__ ---> "+str(point_two.__sub__(point_one)))
    print("__neg__ ---> "+str(point_one.__neg__()))
    print("__neg__ ---> "+str(point_two.__neg__()))
    triangle_one = Triangle(point_one, point_two, point_three)
    print("triangle ---> \n"+str(triangle_one))
    print("triangle AB ---> "+triangle_one.a())
     
if __name__ == "__main__":
    main()

if we look at line 88 - 100, the main method is as follows:

def main():
    point_one = Point(3,5)
    point_two = Point(7,11)
    point_three = Point(6,13)
    print("A ---> "+str(point_one))
    print("B ---> "+str(point_two))
    print("__add__ ---> "+str(point_one.__add__(point_two)))
    print("__sub__ ---> "+str(point_two.__sub__(point_one)))
    print("__neg__ ---> "+str(point_one.__neg__()))
    print("__neg__ ---> "+str(point_two.__neg__()))
    triangle_one = Triangle(point_one, point_two, point_three)
    print("triangle ---> \n"+str(triangle_one))
    print("triangle AB ---> "+triangle_one.a())

Here, every line just works the way i want, except for line 13 which should return the arguments x,y coordinates added(both of type Point()), but Python doesn't. (This particular self-casting is what i hate about Python by the way, str or int you dont know, you can do anything, but can't concatenate an int to a str in a print, ridiculous) print("triangle AB ---> "+triangle_one.a()) prints out triangle AB ---> (3, 5)(7, 11) .
It should print triangle AB ---> (10,16) instead, similar to line 7 in main when adding single points together.
Has someone got an answer for this?

[woooee]

I'm not sure what you are asking, but see if this helps:

## last line under main()
    print "points for one", point_one.x, point_one.y
    print "points for two", point_two.x, point_two.y
#
# and add this additional function to Triangle and call it
    def print_points(self):
        print self.A.x, self.A.y
        print self.B.x, self.B.y
        print self.C.x, self.C.y 
## also under main()
    triangle_one.print_points()

A big part of the problem is lazy naming. How in the hell can you tell what "self.A.x" contains?

[keltik]

I found the problem, it was a cast made by me (to make writing more comfortable) , in one method, i accidentally casted self.A = str(self.A) , whiche messed up everything.
P.S.: I don't like dynamic Typing....

[TrustyTony]

Reconsider about dynamic typing, read this for fun:
http://en.wikipedia.org/wiki/Duck_typing

Otherwise maybe you should start coding in Ada, where you can really 'enjoy' strong typing.:icon_twisted:

Also this thread should then be 'typed' as solved thread, so can you mark it so :)