On non-Windows platforms clock() returns the processor time, perf_counter() does include time elapsed during sleep.

>>> import time
>>> start = time.clock(); time.sleep(1); print(time.clock() - start)
9.700000000001374e-05
>>> start = time.perf_counter(); time.sleep(1); print(time.perf_counter() - start)
1.000714950998372