More arguments

So, how do we pass multiple arguments to a method? Let's add a new method that allows us to move a point to an arbitrary position, not just to the origin. We can also include one that accepts another Point object as input and returns the distance between them:

import math


class Point:
    def move(self, x, y):
        self.x = x
        self.y = y

    def reset(self):
        self.move(0, 0)

 def calculate_distance(self, other_point):
        return math.sqrt(
            (self.x - other_point.x) ** 2
            + (self.y - other_point.y) ** 2
        )


# how to use it:
point1 = Point()
point2 = Point()

point1.reset()
point2.move(5, 0)
print(point2.calculate_distance(point1))
assert point2.calculate_distance(point1) == point1.calculate_distance(
    point2
)
point1.move(3, 4)
print(point1.calculate_distance(point2))
print(point1.calculate_distance(point1))

The print statements at the end give us the following output:

5.0
4.47213595499958
0.0  

A lot has happened here. The class now has three methods. The move method accepts two arguments, x and y, and sets the values on the self object, much like the old reset method from the previous example. The old reset method now calls move, since a reset is just a move to a specific known location.

The calculate_distance method uses the not-too-complex Pythagorean theorem to calculate the distance between two points. I hope you understand the math (**2 means squared, and math.sqrt calculates a square root), but it's not a requirement for our current focus, learning how to write methods.

The sample code at the end of the preceding example shows how to call a method with arguments: simply include the arguments inside the parentheses, and use the same dot notation to access the method. I just picked some random positions to test the methods. The test code calls each method and prints the results on the console. The assert function is a simple test tool; the program will bail if the statement after assert evaluates to False (or zero, empty, or None). In this case, we use it to ensure that the distance is the same regardless of which point called the other point's calculate_distance method.