Nice (abuse of regexp) !

AFAICT the way the string is going to be parsed is equivalent to this:

  def isprime(n):
    if n == 0 or n == 1:
      return False
    i = 2
    while i <= n:
      if (n - i) % i == 0:
        return False
      i += 1
    return True

A parser implementation may optimize and do "while (n - i) >= 1" instead, which cuts in half the number of iterations.