class TriangleError(Exception):

pass

class Triangle(object):

def __init__(self, x, y, z):

self.sides = (x, y, z)

if self._invalid_lengths() or self._violates_inequality():

raise TriangleError

def _invalid_lengths(self):

return any([side <= 0 for side in self.sides])

def _violates_inequality(self):

x, y, z = self.sides

return any([

x + y <= z,

x + z <= y,

y + z <= x,

])

def kind(self):

distinct = len(set(self.sides))

if distinct == 1:

return 'equilateral'

elif distinct == 2:

return 'isosceles'

else:

return 'scalene'