How to call variables from the init method of classes (Python)?

Question

I'm new to programming and I'm confused as to how you call a method/parameter that is defined within a class in Python 2. For example (with obstacle being a previous class made),

class Block(Obstacle):

    def __init__(self, origin, end, detection=9.):
        self.type = 'block'
        self.origin = origin
        self.end = end

        x1 = self.origin[0]
        y1 = self.origin[1]
        x2 = self.end[0]
        y2 = self.end[1]

    def __str__(self):
        return "block obstacle"

When I generate an environment, I define different x1, y1, x2 and y2 values (essentially signifying the coordinate points of the corners of the block). I have another later method where I needs the values of x1, y1, x2 and y2 in calculating something, but I'm confused as to how I actually call them into this new function? What parameters would I put in this new function?

If you define them with self.name they become "global" variables within the class. You could use self.x, self.y = self.origin — Anton vBR
– Anton vBR, Commented Jul 28, 2017 at 11:27
@AntonvBR: I would call them instance variables. Global ones are a different thing... — Serge Ballesta
– Serge Ballesta, Commented Jul 28, 2017 at 11:41
@SergeBallesta You are absolutely right, I couldn't find a better name and hence the citation "" marks. — Anton vBR
– Anton vBR, Commented Jul 28, 2017 at 12:26

Zero Piraeus · Accepted Answer · 2017-09-11 16:36:41Z

import math

I would make x1 --> self.x1 so you can have it as an object variable.

Inside the class object you can define these functions for calculation as an example.

def calculate_centre(self):
    self.centre_x = self.x2 - self.x1
    self.centre_y = self.y2 - self.y1

    self.centre = (centre_x, centre_y)

def distance_between_block_centres(self, other):
    block_x, block_y  = other.centre

    distance = math.sqrt((self.centre_x - block_x)**2 + (self.centre_y - block_y)**2)
    return distance 


block = Block(stuff)
block_2 = Block(other_stuff)

if you want to call these function using the objects youve created:

block.calculate_centre()
block_2.calculate_centre()
distance_between = block.distance_between_block_centres(block_2)

And even external to your object call the variables:

print block.centre
#>>> (3, 5)

Lastly you can run the calculations of the centre without having to call it every time you create your object if your put it in def __init__():

self.calculate_centre()

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