Question

I came across the following solution for this problem: http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-00-introduction-to-computer-science-and-programming-fall-2008/assignments/pset1a.pdf :


def testPrime(x):
factor = 2
while factor**2 <= x:
if x % factor == 0:
return False
else:
factor = factor + 1

return True

candidate = 3
numPrime = 1

while numPrime < 1000:
if testPrime(candidate):
numPrime = numPrime + 1
candidate = candidate + 2

print "The 1000th prime number is", candidate - 2


I'm having a hard time understanding what's going on here, and was totally lost on the problem in the first place. How can I wrap my mind around this?

Answer 1

Without anything specific to address I will offer this, hopefully it helps.

The first section of this code is defining a function, this is the meat of the program as it will be the part that does all of the work:
def testPrime(x): // Define the name and input var of our function
factor = 2 // Assign the variable an initial value
while factor**2 <= x: // As long as our factor *2 is less than or equal to x, keep going
if x % factor == 0: // If x divided by our factor has a remainder of 0, do this
return False
else: // Otherwise do this
factor = factor + 1
return True

/* Define two variables and give values */
candidate = 3
numPrime = 1

while numPrime < 1000: // While variable numPrime is less than 1000, keep going
if testPrime(candidate): // If the function testPrime returns a true, do this
numPrime = numPrime + 1
candidate = candidate + 2
/* Print the results */
print "The 1000th prime number is", candidate - 2

Answer 2

Awesome documentation eSpeX. This shows how important it is to learn to read code as well as to write it. You've done this before.