Rational Numbers

Write a class Rational to represent a rational number p/q, where both p and q are integers, and by definition the denominator q should not be equal to 0. Your class should implement the following methods:
  1. __init__(self, p, q) Creates a rational number and stores p, q as the numerator and denominator, respectively.
  2. reduce(self) Calculates the greatest common divisor (gcd) of the numerator and the denominator, and divide them by gcd. For example, after the reduction, 24/36 becomes 2/3.
  3. __str__(self) Return a string representing the rational number with the format p/q. If q is equal to 1, you may omit the portion of "/q" and simply return the portion for "p".
You may test your class with the following main program: 

def main():
    a = Rational(24, 36)
    print(a)
    a.reduce()
    print(a)

if __name__ == "__main__":
    main()
The result may look like: 

24/36
2/3