Get timer ticks in Python

问题:

I'm just trying to time a piece of code. The pseudocode looks like:

start = get_ticks()
do_long_code()
print "It took " + (get_ticks() - start) + " seconds."

How does this look in Python?

More specifically, how do I get the number of ticks since midnight (or however Python organizes that timing)?

回答1:

In the time module, there are two timing functions: time and clock. time gives you "wall" time, if this is what you care about.

However, the python docs say that clock should be used for benchmarking. Note that clock behaves different in separate systems:

• on MS Windows, it uses the Win32 function QueryPerformanceCounter(), with "resolution typically better than a microsecond". It has no special meaning, it's just a number (it starts counting the first time you call clock in your process).

    # ms windows
    t0= time.clock()
    do_something()
    t= time.clock() - t0 # t is wall seconds elapsed (floating point)

• on *nix, clock reports CPU time. Now, this is different, and most probably the value you want, since your program hardly ever is the only process requesting CPU time (even if you have no other processes, the kernel uses CPU time now and then). So, this number, which typically is smaller¹ than the wall time (i.e. time.time() - t0), is more meaningful when benchmarking code:

    # linux
    t0= time.clock()
    do_something()
    t= time.clock() - t0 # t is CPU seconds elapsed (floating point)

Apart from all that, the timeit module has the Timer class that is supposed to use what's best for benchmarking from the available functionality.

¹ unless threading gets in the way…

² Python ≥3.3: there are time.perf_counter() and time.process_time(). perf_counter is being used by the timeit module.

回答2:

What you need is time() function from time module:

import time
start = time.time()
do_long_code()
print "it took", time.time() - start, "seconds."

You can use timeit module for more options though.

回答3:

Here's a solution that I started using recently:

class Timer:
    def __enter__(self):
        self.begin = now()

    def __exit__(self, type, value, traceback):
        print(format_delta(self.begin, now()))

You use it like this (You need at least Python 2.5):

with Timer():
    do_long_code()

When your code finishes, Timer automatically prints out the run time. Sweet! If I'm trying to quickly bench something in the Python Interpreter, this is the easiest way to go.

And here's a sample implementation of 'now' and 'format_delta', though feel free to use your preferred timing and formatting method.

import datetime

def now():
    return datetime.datetime.now()

# Prints one of the following formats*:
# 1.58 days
# 2.98 hours
# 9.28 minutes # Not actually added yet, oops.
# 5.60 seconds
# 790 milliseconds
# *Except I prefer abbreviated formats, so I print d,h,m,s, or ms. 
def format_delta(start,end):

    # Time in microseconds
    one_day = 86400000000
    one_hour = 3600000000
    one_second = 1000000
    one_millisecond = 1000

    delta = end - start

    build_time_us = delta.microseconds + delta.seconds * one_second + delta.days * one_day

    days = 0
    while build_time_us > one_day:
        build_time_us -= one_day
        days += 1

    if days > 0:
        time_str = "%.2fd" % ( days + build_time_us / float(one_day) )
    else:
        hours = 0
        while build_time_us > one_hour:
            build_time_us -= one_hour
            hours += 1
        if hours > 0:
            time_str = "%.2fh" % ( hours + build_time_us / float(one_hour) )
        else:
            seconds = 0
            while build_time_us > one_second:
                build_time_us -= one_second
                seconds += 1
            if seconds > 0:
                time_str = "%.2fs" % ( seconds + build_time_us / float(one_second) )
            else:
                ms = 0
                while build_time_us > one_millisecond:
                    build_time_us -= one_millisecond
                    ms += 1
                time_str = "%.2fms" % ( ms + build_time_us / float(one_millisecond) )
    return time_str

Please let me know if you have a preferred formatting method, or if there's an easier way to do all of this!

回答4:

The time module in python gives you access to the clock() function, which returns time in seconds as a floating point.

Different systems will have different accuracy based on their internal clock setup (ticks per second) but it's generally at least under 20milliseconds, and in some cases better than a few microseconds.

-Adam

回答5:

import datetime

start = datetime.datetime.now()
do_long_code()
finish = datetime.datetime.now()
delta = finish - start
print delta.seconds

From midnight:

import datetime

midnight = datetime.datetime.now().replace(hour=0, minute=0, second=0, microsecond=0)
now = datetime.datetime.now()
delta = now - midnight
print delta.seconds

回答6:

If you have many statements you want to time, you could use something like this:

class Ticker:
    def __init__(self):
        self.t = clock()

    def __call__(self):
        dt = clock() - self.t
        self.t = clock()
        return 1000 * dt

Then your code could look like:

tick = Ticker()
# first command
print('first took {}ms'.format(tick())
# second group of commands
print('second took {}ms'.format(tick())
# third group of commands
print('third took {}ms'.format(tick())

That way you don't need to type t = time() before each block and 1000 * (time() - t) after it, while still keeping control over formatting (though you could easily put that in Ticket too).

It's a minimal gain, but I think it's kind of convenient.