Class Methods

Question

Trying to get a program to print the perimeter of a triangle. I borrowed from the class methods module to practice and added/changed as needed. Says error in line 13 is "undefined" but I cannot figure out why? Any ideas?

class triangle:
def __init__(self, left, right, bottom):
self_left = left
self_right = right
self_bottom = bottom

def calculate_perimeter(self):
return self_left + self_right + self_bottom

@classmethod
def new_tri(cls, perimeter):
return cls(self_left + self_right + self_bottom)

perimeter = triangle.new_tri(5)
print(perimeter.calculate_perimeter())

Answer 1

You need to define the attributes of an instance with self._left.

If you leave out the dot, self_left is just a regular variable and will be deleted after the end of init.

Also you need to understand that a class method doesn't know 'self' because a class method gets the *class* as first argument, not 'self'.

From what I see, I'd recommend to practice with regular methods in simple cases a bit more, since there are still deficits. Do class methods after you firmly understood the basics of how classes work.