What's the most efficient way to sleep in Python?

Question

What would be better ?

time.sleep(delayTime)

or

select.select([],[],[],delayTime)

Are they equivalent ? Is select more efficient?

Answer 1

The answer depends on what your trying to achieve:

time.sleep(delayTime)

• Action: Suspend execution of the current thread for the given number of seconds.
• Any caught signal will terminate the sleep() following execution of that signal's catching routine

select.select([],[],[],delayTime)

This is a straightforward interface to the Unix select() system call. The first three arguments are sequences of 'waitable objects':

• rlist : wait until ready for reading
• wlist : wait until ready for writing
• xlist : wait for an “exceptional condition”

So now, that we understand the two interfaces we can understand that the answer depends on the purpose:
If all you want to do is to suspend the current thread - the first option is simpler. But if there are objects to wait on - use the second method. In temp of efficiency - I don't think there are differences if all you are looking for is the simplest use-case (just suspend the main thread).

Answer 2

Pretty simple to hackup a test in python with called to timeit , but I love ipython for quick tests ( http://ipython.org/ ). Here's my results:

$ ipython
import time,select

%timeit time.sleep(0)
1000000 loops, best of 3: 655 ns per loop

%timeit select.select([],[],[],0)
1000000 loops, best of 3: 902 ns per loop

But if you don't have access to ipython, and would prefer native timeit from command line:

$ python -m timeit -s "import time,select" "time.sleep(0)"
1000000 loops, best of 3: 0.583 usec per loop

$ python -m timeit -s "import time,select" "select.select([],[],[],0)"
1000000 loops, best of 3: 0.777 usec per loop

Answer 3

How you defining the efficiency? In most of the cases, the sleep and select have been using to observe if there space/buffer. If the space is not available, then we have option to wait and see when the buffer will be empty and we can execute our action. The sleep() internally select(). So, I think it matters with which you are comfortable with, I guess.