试图理解这个简单的python代码

Question

I was reading Jeff Knupp's blog and I came across this easy little script:

import math

def is_prime(n):
    if n > 1:
        if n == 2:
            return True
        if n % 2 == 0:
            return False
        for current in range(3, int(math.sqrt(n) + 1), 2):
            if n % current == 0:
                return False
        return True
    return False

print(is_prime(17))

(note: I added the import math at the beginning. You can see the original here: http://www.jeffknupp.com/blog/2013/04/07/improve-your-python-yield-and-generators-explained/ )

This is all pretty straightforward and I get the majority of it, but I'm not sure what's going on with his use of the range function. I haven't ever used it this way or seen anyone else use it this way, but then I'm a beginner. What does it mean for the range function to have three parameters, and how does this accomplish testing for primeness?

Also (and apologies if this is a stupid question), but the very last 'return False' statement. That is there so that if a number is passed to the function that is less than one (and thus not able to be prime), the function won't even waste its time evaluating that number, right?

Answer 1

The third is the step. It iterates through every odd number less than or equal to the square root of the input (3, 5, 7, etc.).

Answer 2

import math #import math module

def is_prime(n): #define is_prime function  and assign variable n to its argument (n = 17 in this example).
    if n > 1: #check if n (its argument) is greater than one, if so, continue; else return False (this is the last return in the function).
        if n == 2: #check if n equals 2, it so return True and exit.
            return True
        if n % 2 == 0: #check if the remainder of n divided by two equas 0, if so, return False (is not prime) and exit. 
            return False
        for current in range(3, int(math.sqrt(n) + 1), 2): #use range function to generate a sequence starting with value 3 up to, but not including, the truncated value of the square root of n, plus 1. Once you have this secuence give me every other number ( 3, 5, 7, etc)     
            if n % current == 0: #Check every value from the above secuence and if the remainder of n divided by that value is 0, return False (it's not prime)
                return False
        return True #if not number in the secuence divided n with a zero remainder then n is prime, return True and exit.  
    return False

print(is_prime(17))