17.5, 17.6: Constructers and Methods¶

17.5 Improving our Constructor¶

Our constructor so far can only create points at location (0,0)
To create a point at position (7, 6) requires that we provide some additional capability for the user to pass information to the constructor.
Since constructors are simply specially named functions, we can use parameters (as we’ve seen before) to provide the specific information.
We can make our class constructor more general by putting extra parameters into the __init__ method: self.x = initX & self.y = inity

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
p = Point(7, 6)

Now when we create new points, we supply the x and y coordinates as parameters. When the point is created, the values of initX and initY are assigned to the state of the object.

17.6 Adding other Methods (kinda functions) to our Class¶

Rather than using a tuple for our points, (7, 6) , we can use the Point class we made to add methods for operations on the points given
Creating a class like Point brings an exceptional amount of “organizational power” to our programs, and to our thinking.
A method behaves like a function but it is invoked on a specific instance.
For example, with a turtle named tess, tess.right(90) asks the tess object to perform its right method and turn 90 degrees
Methods are accessed using dot notation.

Example:¶

The getX method, when invoked, will return the value of the x coordinate.
- The implementation of this method is straight forward since we already know how to write functions that return values

Even though the get X method does not need any other parameter information to do its work, there is still one formal parameter, self

All methods defined in a class that operate on objects of that class will have self as their first parameter.

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


p = Point(7, 6)
print(p.getX())
print(p.getY())

Output: 7 6

Note that the getX & getY method simply returns the value of self.x & self.y from the object itself.
- In other words, the implementation of the method is to go to the state of the object itself and get the value of x & y
Example:
Let’s add another method, distanceFromOrigin

This method will again not need any additional information to do its work.

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.distanceFromOrigin())

9.219544457292887

Notice that the caller of distanceFromOrigin does not explicitly supply an argument to match the self parameter.
This is true of all method calls