Python script to compute modular-exponentiation recursively.

modular_exponentiation_2.py

#! /usr/local/bin/python3.6
"""
Modular Exponentiation (recursive)
"""
import sys
import traceback


class ModularExponentiation:
    def comp_mod_exp(self, b, e, m):
        """ Computation of modular exponentiation

        :param  int  b: base
        :param  int  e: exponent
        :param  int  m: modulus
        :return int me: modular expornentiation
        """
        try:
            if e == 0:
                return 1
            ans = self.comp_mod_exp(b, e // 2, m)
            ans = (ans * ans) % m
            if e % 2 == 1:
                ans = (ans * b) % m
            return ans
        except Exception as e:
            raise


if __name__ == '__main__':
    # me = b^e mod m
    b, e, m = 12345, 6789, 4567
    try:
        obj = ModularExponentiation()
        me = obj.comp_mod_exp(b, e, m)
        print("{}^{} mod {} = {}".format(b, e, m, me))
    except Exception as e:
        traceback.print_exc()
        sys.exit(1)

what if b is negative ??