Rui Maciel wrote:
> Let:
> - class Point be a data type which is used to define points in space
> - class Line be a data type which possesses an aggregate relationship with
> objects of type Point
> - class Model be a container class which stores collections of Point and
> Line objects
>
>
> Essentially, a Model object stores lists of Point objects and Line
> objects, and Line objects include references to Point objects which
> represent the starting and ending point of a line.
>
> To reflect this class relationship, I've defined the following classes:
>
> <code>
> class Point:
Don't add
> position = []
to your code. That's not a declaration, but a class attribute and in the
long run it will cause nothing but trouble.
> def __init__(self, x, y, z = 0):
> self.position = [x, y, z]
>
> class Line:
> points = ()
> def __init__(self, p_i, p_f):
> self.points = (p_i, p_f)
>
> class Model:
> points = []
> lines = []
>
>
> </code>
>
> It would be nice if, whenever a Point object was updated, the Line objects
> which are associated with it could reflect those updates directly in
> Line.p_i and Line.p_f.
>
> What's the Python way of achieving the same effect?
Your code already does that. Here's a minimally cleaned up version:
$ cat tmp_points.py
class Point:
def __init__(self, x, y, z=0):
self.position = (x, y, z)
def __str__(self):
return "%s" % (self.position,)
class Line:
def __init__(self, p_i, p_f):
self.points = (p_i, p_f)
def __str__(self):
return "%s-->%s" % self.points
a = Point(1, 2, 3)
b = Point(4, 5, 6)
ab = Line(a, b)
print(ab)
a.position = (10, 20, 30)
print(ab)
$ python3 tmp_points.py
(1, 2, 3)-->(4, 5, 6)
(10, 20, 30)-->(4, 5, 6)
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