Project Euler Challenge 7

Euler7.py

"""You'll have to forgive me some of the ugly,
   I wrote this when I was new to Python, but it looks passable.
       -r3
"""

def is_prime(num):
    """Checks argument for primality"""

    # Optimization to determine if even
    if num % 2 == 0:
        return False

    # From there on out, we can just check odds
    div = 3
    while div <= (num * num):
        if not num % div:
            return False
        div += 2

    return True

def prime_gen(start=2):
    """Produces prime numbers

    Returns an iterable generator for 
    consecutive increasing primes 
    starting with the optional argument.
    Default start is 2, the lowest prime.
    """

    # Again, checking for evens first
    if start == 2:
        # Notice the multiple yeild statements here?
        # Execution will "pause" on each, yielding the value and "continue"
        # execution when asked for the next prime
        yield 2
        yield 3
        start += 3

    # Moving on to the heart of the matter... Checking odds.
    while True:
        if is_prime(start):
            yield start
        elif start % 2 == 0:
            start += 1
        start += 2

if __name__ == '__main__':
    # `enumerate` is one you may not have seen before; it turns each value in an
    # iterable into a tuple pair: (0, n), (1, n+1), (2, n+2), (3, n+3) ...
    # The leading value in the pair is the index with the usual return value of the
    # iterable as 'n'. This allows us to check if the count (index + 1) has reached our
    # desired prime. The `enumerate` gets rid of the ugly but common idiom:
    # for ix in range(len(var)) => for ix, _ in enumerate(var)
    # Note that the '_' character is idiomatic for vars that you'll not be using and is
    # otherwise a valid variable.
    for count, prime in enumerate(prime_gen()):
        if count + 1 == 10001:
            print prime
            break