Newbie to python-- problem on Object Oriented Programming

Question

I worked on using the slope and the distance formula here. But I think indexing is the wrong approach, or is it?

class Line():
 def __init__(self,coord1,coord2):
 self.coord1 = coord1
 self.coord2 = coord2
 def distance(self):
 return ((coord2[0]-coord1[0])**2 + (coord2[1]-coord1[1])**2)**0.5
 def slope(self):
 return (coord2[1] - coord1[1])/(coord2[0]-coord1[0])

Answer 1

To access the class specific variables you need to use self.#varibale name So your functions should look like this:

 def distance(self):
 return ((self.coord2[0]-self.coord1[0])**2 + (self.coord2[1]-self.coord1[1])**2)**0.5
 def slope(self):
 return (self.coord2[1] - self.coord1[1])/(self.coord2[0]-self.coord1[0])

Answer 2

Assuming coord is a tuple I prefer to unpack them first for readability:

def slope(self):
 x1,y1 = self.coord1
 x2,y2 = self.coord2
 return (y2 - y1)/(x2-x1)

Answer 3

There's nothing wrong with indexing. You might find it more readable if you provide more descriptive names for the components. For example,

def distance(self):
 c1x = self.coord1[0]
 c1y = self.coord1[1]
 c2x = self.coord2[0]
 c2y = self.coord2[1]
 return ((c2x - c1x)**2 + (c2y - c1y)**2)**0.5

which you can make less verbose with tuple unpacking:

def distance(self):
 c1x, c1y = self.coord1
 c2x, c2y = self.coord2
 return ((c2x - c1x)**2 + (c2y - c1y)**2)**0.5

and even less verbose by working on the complex plane:

def distance(self):
 return abs(complex(**self.coord2) - complex(**self.coord1))

(For slope, the complex-number trick involves converting the difference between the two to polar coordinates with cmath.polar.)

• Mourya: what is the use of "complex"?
• chepner: It creates a complex number from the coordinate pair, e.g (3, 0) becomes 3+0j. Since complex numbers can be views as points in the complex plane, the distance between two complex numbers is just the magnitude of the vector defined by two points, which is just the absolute value of the difference of two complex numbers. You basically get the squaring and square root for free.
• chepner: For example, abs(complex(3,0) - complex(0,4)) == abs(3 - 4j) == 5.0.