17.7, 17.8, 17.9: Objects, Strings, Return Values¶

17.7 Objects as Arguements and Parameters¶

You can use the object/classes as arguments in a functions

Function calling the Point object we created:

def distance(point1, point2):
    xdiff = point2.getX() - point1.getX()
    ydiff = point2.getY() - point1.getY()

    dist = math.sqrt(xdiff**2 + ydiff**2)
    return dist

p = Point(4, 3)
q = Point(0, 0)
print(distance(p, q))

5.0

distance takes two points and returns the distance between them.
Note that distance is not a method of the Point class, it is a standalone function.

17.8 Converting an Object to a String¶

When we’re working with classes and objects, it is often necessary to print an object (that is to print the state of an object).

Example¶

The default print statement for an object is to tell you the type the object is.

class Point:
    """ Point class for representing and manipulating x,y coordinates. """

    def __init__(self, initX, initY):
        """ Create a new point at the given coordinates. """
        self.x = initX
        self.y = initY

    def getX(self):
        return self.x

    def getY(self):
        return self.y

    def distanceFromOrigin(self):
        return ((self.x ** 2) + (self.y ** 2)) ** 0.5


p = Point(7, 6)
print(p)

<main.Point object>

It does not tell you anything about the specific state of the point.
We can improve on this representation if we include a special method call __str__ in the Point object/class
_str__ method is responsible for returning a string representation as defined by the class creator.

You as the programmer, get to choose what a Point should look like when it gets printed.

class Point:
    """ Point class for representing and manipulating x,y coordinates. """

    def __init__(self, initX, initY):
        """ Create a new point at the given coordinates. """
        self.x = initX
        self.y = initY

    def getX(self):
        return self.x

    def getY(self):
        return self.y

    def distanceFromOrigin(self):
        return ((self.x ** 2) + (self.y ** 2)) ** 0.5

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

p = Point(7, 6)
print(p)

x=7, y=6

17.9 Instances as Return Values¶

Functions and methods can return objects (Obviously)
Example: Have a point object and wish to find the midpoint halfway between it and some other target point.

Method, called halfway that takes another Point as a parameter and returns the Point that is halfway between the point and the target.

class Point:

    def __init__(self, initX, initY):
        """ Create a new point at the given coordinates. """
        self.x = initX
        self.y = initY

    def getX(self):
        return self.x

    def getY(self):
        return self.y

    def distanceFromOrigin(self):
        return ((self.x ** 2) + (self.y ** 2)) ** 0.5

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

    def halfway(self, target):
        mx = (self.x + target.x) / 2
        my = (self.y + target.y) / 2
        return Point(mx, my)

p = Point(3, 4)
q = Point(5, 12)
mid = p.halfway(q)

print(mid)
print(mid.getX())
print(mid.getY())

x=4.0, y=8.0 4.0 8.0