Timing Module

Luckily, Python makes it easy to time code. To see how the iteration options stack up, let’s start with a simple but general timer utility function coded in a module file, so it can be used in a variety of programs:

# File mytimer.py

import time
reps = 1000
repslist = range(reps)

def timer(func, *pargs, **kargs):
    start = time.clock()
    for i in repslist:
        ret = func(*pargs, **kargs)
    elapsed = time.clock() - start
    return (elapsed, ret)

广告：个人专属 VPN，独立 IP，无限流量，多机房切换，还可以屏蔽广告和恶意软件，每月最低仅 5 美元

Operationally, this module times calls to any function with any positional and keyword arguments by fetching the start time, calling the function a fixed number of times, and subtracting the start time from the stop time. Points to notice:

 

 
  • Python’s time module gives access to the current time, with precision that varies per platform. On Windows, this call is claimed to give microsecond granularity and so is very accurate.
  • The range call is hoisted out of the timing loop, so its construction cost is not charged to the timed function in Python 2.6. In 3.0 range is an iterator, so this step isn’t required (but doesn’t hurt).
  • The reps count is a global that importers can change if needed: mytimer.reps = N.

When complete, the total elapsed time for all calls is returned in a tuple, along with the timed function’s final return value so callers can verify its operation.

From a larger perspective, because this function is coded in a module file, it becomes a generally useful tool anywhere we wish to import it. You’ll learn more about modules and imports in the next part of this book—simply import the module and call the function to use this file’s timer (and see Chapter 3’s coverage of module attributes if you need a refresher).