"""
Simple no bells and whistles rational number
class used to help students with "__rib__ syntax"
i.e. triggering specially named functions like
__add__ using the + operator.

Placed in the public domain by:
Kirby Urner
Saturday Academy
Silicon Forest, Oregon

Usage:

>>> from rationals import Rat
>>> somerat = Rat(2,3)
>>> otherat = Rat(5,12)
>>> somerat + otherat
(13/12)
>>> somerat * Rat(3,2)
(1/1)
>>> somerat * otherat
(5/18)
"""

def gcd(a,b):
    """
    Euclid's Algorithm
    """
    while b:
	a, b = b, a%b
    return a

def lcm(a,b):
    return (a*b)/gcd(a,b)


class Rat:
    """
    Bare bones Rational; feel free to enhance (e.g. __pow__)
    """

    def __init__(self, numer, denom):
	"""reduce to lowest terms at birth"""
	thegcd = gcd(numer, denom) # gcd a global
	self.numer = numer/thegcd
	self.denom = denom/thegcd
		
    def __add__(self, other):
        """add using common denominator"""
	commondenom = lcm(self.denom, other.denom) # lcm a global
	newnumera = (commondenom/self.denom)*self.numer
	newnumerb = (commondenom/other.denom)*other.numer
	return Rat(newnumera + newnumerb, commondenom)

    def __neg__(self):
        return Rat(-self.numer, self.denom)

    def __sub__(self, other):
        return self + (-other)
    
    def __mul__(self, other):
	"""multiplying is easier..."""
	return Rat(self.numer * other.numer,
                   self.denom*other.denom)

    def __div__(self, other):
        """multiply by reciprocal (= mult. inverse)"""
        return Rat(self.numer * other.denom,
                   other.numer * self.denom)

    def __repr__(self):
	"""show me!"""
	return "(%s/%s)" % (self.numer, self.denom)

def testit():
    somerat = Rat(2,3)
    otherat = Rat(5,12)
    print somerat
    print otherat
    print "%s + %s = %s" % (somerat, otherat, somerat + otherat)
    print "%s - %s = %s" % (somerat, otherat, somerat - otherat)
    print "%s * %s = %s" % (somerat, otherat, somerat * otherat)
    print "%s / %s = %s" % (somerat, otherat, somerat / otherat)
    print "- %s = %s" % (somerat, -somerat)
    
if __name__ == "__main__":
    testit()