Question

I’m running Python 3.2 on a Windows 7 OS in WingIDE 101(Version 4). The environment doesn’t really matter in this case, but I figured I should be specific.

My code is as follows. It is not meant to be optimal, just one way to find a prime number:

def isPrime2(n):
  if n == 1:
      return False  
  count = 0
  for i in range(2,n+1,2):
    if n%i == 0:
      count = count + 1
      if count > 2:
        return False
  for i in range(1,n+1,2):
    if n%i == 0:
      count = count + 1
      if count > 2:
        return False         
  if count == 2:
    return True

start = time.time()
x = isPrime2(571)
end = time.time()
time_interval = end - start
print("%1.15f"%time_interval)
print(x)

The problem I am having is that the time.time() function doesn’t seem to be timing. When I run this program I get

0.000000000000000
True

I also tried this up to 30 digits and all of them remained zero.

There is no way my program is this fast considering that I have multiple For loops.

My question is, why is my function not being timed? Or if it is, why is it so fast when I know it should not be?

Answer 1

On Windows, you want to use time.clock() instead; time.time() only has 1/60th-second granularity, while the former gives you microsecond granularity instead.

Or, to keep it cross-platform, use timeit.default_timer() instead, which will use the correct time function for your platform:

import timeit

start = timeit.default_timer()