DouKaku?

def gcd(m, n):
    assert m > 0
    assert n > 0
    while n:
        m, n = n, m % n
    assert m > 0
    return m

class Rational:
    def __init__(self, b, c):
        g = gcd(b, c)
        self.b = b // g
        self.c = c // g

    def __repr__(self):
        return "%d/%d" % (self.b, self.c)

    def __cmp__(self, that):
        return self.b * that.c - self.c * that.b

    def value(self):
        return float(self.b) / self.c

def rationalize(a):
    rationals = []
    for c in xrange(1, 10):
        b = int(a * c + 0.5)
        r = Rational(b, c)
        if r.b == b:
            rationals.append(r)
    rationals.sort(key=lambda r: abs(a - r.value()))
    return rationals

def solve(a):
    print "a = %f" % a, " ".join(repr(r) for r in rationalize(a))

def main():
    solve(1.732051)
    solve(3.141593)
    solve(1920.0 / 1080)

if __name__ == '__main__':
    main()