decimal_period.py

# Does the decimal expansion of 1/q terminate?
def terminates(q):
	while q % 2 == 0:
		q //= 2
	while q % 5 == 0:
		q //= 5
	return q == 1

# If the decimal expansion of 1/q terminates return 0, else return the period of the repeating digits.
def period(q):
	if terminates(q):
		return 0
	rems = []
	p = 1
	i = 0
	while True:
		rem = p % q
		if rem in rems:
			return i - rems.index(rem)
		i += 1
		rems.append(rem)
		p = 10 * rem