Class, object question.

[Ian Sparks]

Use the *args positional-argument to catch all the positional arguments in the constructor then test them to see what you have and call a kind of sub-init based on that :

class Point:
    def __init__(self,x,y,z):
        self.x = x
        self.y = y
        self.z = z
 
class Vector:
    def __init__(self,*args):
        if len(args) == 3:
            self.setFromValues(args)
        elif len(args) == 2:
            if isinstance(args[0],Point):
                self.setFromPoints(args)
        else:
            raise "Incorrect constructor"
                
        print self.i,self.j,self.k
 
    def setFromValues(self,args):
        self.i,self.j,self.k = args
 
    def setFromPoints(self,args):
        self.i = args[1].x - args[0].x
        self.j = args[1].y - args[0].y
        self.k = args[1].z - args[0].z
 
v = Vector(1,2,3)
 
p1 = Point(2,2,2)
p2 = Point(4,4,4)
 
v2 = Vector(p1,p2)
 
 Hope this helps.
 
 
 
 -----Original Message-----
From: Jeffrey Maitland [mailto:maitj at vianet.ca]
Sent: Tuesday, April 05, 2005 10:04 AM
To: python-list at python.org
Subject: Class, object question.



Hello folks, 

 

The question I am having is something like this. 

 

# ignore the precursing ....  I am using them for easy message formatting

 

from point import *

 

Class vector(point): 

..........def __init___(self, point1, point2):

.................self.i = point2.get_x() - point1.get_x()

.................self.j = point2.get_y() - point1.get_y()

.................self.k =  point2.get_z() - point1.get_z()

 

# methods of vector. Defined here. 

 

What I am wondering is if I have a 2nd init  or something similar to create a vector. Such as what follows and if I can how do I go about implementing it?

 

Class vector(point): 

..........def __init___(self, point1, point2):

.................self.i = point2.get_x() - point1.get_x()

.................self.j = point2.get_y() - point1.get_y()

.................self.k =  point2.get_z() - point1.get_z()

.

..........def __init___(self, i, j, k):

.................self.i = i

.................self.j = j

.................self.k = k

 

That way I can define a vector either using 2 points or if I have the vector data itself?

 

Thanks in advance

 

Jeff

 

 

 

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