Project Euler-Problem #37

PythonEuler37.py

def divides(k,n):
	"""
	Determines if number n is divisible by n
	"""
	return n % k == 0

def ldf(n, k):
	"""
	Obtains the least divisor of n starting from k.
	"""
	while True:
		if divides(k, n): 
			return k
		elif k ** 2 > n:
			return n
		else:
			k += 1

def ld(n):
	"""
	Obtains the least divisor of n starting from 2.
	"""
	return ldf(n, 2)

def is_prime(n):
	"""
	Determines whether a number is prime or not.
	"""
	if n < 2:
		return False
	return ld(n) == n

def from_left(prime):
	"""
	Evaluates if a prime number is truncable from left.
	"""
	s = str(prime)
	for i in range(1,len(s)):
		if not is_prime(int(s[i:])):
			return False
	return True

def from_right(prime):
	"""
	Evaluates if a prime number is truncable from right.
	"""
	s = str(prime)
	for i in range(-1,-len(s),-1):
		if not is_prime(int(s[0:i])):
			return False
	return True	

def next_prime():
	"""
	Obtains the next truncable prime.
	"""
	n = 11
	while True:
		if is_prime(n) and from_left(n) and from_right(n):
			yield n
		n += 2

def solve():
	primes = []
	for prime in next_prime():
		primes.append(prime) 
		if len(primes) == 11:
			break
	return sum(primes)

print "The sum of first 11 truncable primes is: %d " % solve()