Python Calculator

calc.py

#! /usr/bin/python3

import unittest

class NegativeNumber(Exception):
    pass

class Calculator:
    def add(self, numbers: str) -> int:
        self.negatives = []

        if (len(numbers) == 0):
            return 0

        delimiter = ","

        if (numbers.startswith("//")):
            pieces = numbers.split("\n")
            # take delimiter on first line
            delimiter = pieces[0].replace("//", "")
            print("delimiter", delimiter)
            # normalize input to replace all newlines by the specified delimiter to avoid regexps
            numbers = delimiter.join(pieces[1:])
        else:
            # normalize input to replace all newlines by the specified delimiter to avoid regexps
            numbers = numbers.replace("\n", delimiter)

        print("numbers", numbers)
        array_strings = numbers.split(delimiter)
        print("array_strings", array_strings)
        nb = sum([self.toint(x) for x in array_strings])

        if len(self.negatives) > 0:
            raise NegativeNumber("Negatives are not allowed: %s" % ", ".join(self.negatives))

        return nb

    def toint(self, x):
        xx = int(x)
        if (xx < 0):
            self.negatives.append(x)
        if (xx > 1000):
            return 0
        return xx

class Test(unittest.TestCase):
    def testCalculator(self):
        calc = Calculator()
        self.assertEqual(0, calc.add(""))
        self.assertEqual(1, calc.add("1"))
        self.assertEqual(3, calc.add("1\n2"))
        self.assertEqual(6, calc.add("1\n2,3"))

        try:
            calc.add("1,\n")
        except ValueError:
            # This is OK
            pass

        self.assertEqual(6, calc.add("//+\n1+2+3"))
        self.assertEqual(6, calc.add("//\\\n1\\2\\3"))

        try:
            calc.add("-1")
        except NegativeNumber as e:
            self.assertEqual("Negatives are not allowed: -1", str(e))

        try:
            calc.add("-1,0,-2")
        except NegativeNumber as e:
            self.assertEqual("Negatives are not allowed: -1, -2", str(e))

        self.assertEqual(6, calc.add("1,2,1001,3"))

        # 7. delimiter in any format
        self.assertEqual(6, calc.add("//***\n1***2***3"))

if __name__ == '__main__':
    unittest.main()