main.py

from enum import Enum

from kivy.app import App
from kivy.properties import StringProperty


class Classification(Enum):
    INVALID = 'Invalid'
    EQUILATERAL = 'Equilateral'
    ISOSCELES = 'Isosceles'
    RIGHT = 'Right'
    SCALENE = 'Scalene'


class TriangleApp(App):
    a = StringProperty('')
    b = StringProperty('')
    c = StringProperty('')
    classification = StringProperty()

    @staticmethod
    def classify(a, b, c):  # buggy
        if a * b * c < 0:
            return Classification.INVALID
        if a == b and b == c:
            return Classification.EQUILATERAL
        if a == b or b == c:
            return Classification.ISOSCELES
        maximum = a
        if b > maximum:
            maximum = b
            if c > maximum:
                maximum = c
        semiperimeter = a + b + c / 2
        if maximum > semiperimeter:
            return Classification.INVALID
        if a ** 2 + b ** 2 == c ** 2 or b ** 2 + a ** 2 == c ** 2 or c ** 2 + b ** 2 == a ** 2:
            return Classification.RIGHT
        return Classification.SCALENE

    def update(self):
        try:
            self.classification = TriangleApp.classify(int(self.a), int(self.b), int(self.c)).value
        except ValueError:
            self.classification = f'{Classification.INVALID.value} (non-integer sides)'

    def on_start(self):
        self.update()

    def on_a(self, _, __):
        self.update()

    def on_b(self, _, __):
        self.update()

    def on_c(self, _, __):
        self.update()


if __name__ == '__main__':
    app = TriangleApp()
    app.run()