在初學python的階段，筆者曾使用裝飾器來實現計算程式執行的時間。慢慢地才知道，python中有更方便的模組——timeit，在本文結束後，筆者會把timeit原始碼附帶，只有短短的一百多行，so easy，大家都應該能讀懂原始碼。那就直接看使用吧！

基本用法

import timeit


# 待測試的函式
def add():
    return sum(range(111))


# stmt 需要測試的函式或語句，字串形式
# setup 執行的環境，本例子中表示 if __name__ == '__main__':
# number 被測試的函式或語句，執行的次數，本例表示執行100000次add()。省缺則預設是10000次
# 綜上：此函式表示在if __name__ == '__main__'的條件下，執行100000次add()消耗的時間
t = timeit.timeit(stmt="add()", setup="from  __main__ import add", number=100000)
print(t)
 

那麼如果當下有這樣的需求：測試add函式執行100k的時間，且把測試100遍，然後求平均值。timeit無論每次測試執行多少變，但這個測試只進行一遍。有的小夥伴說可以使用for 迴圈100次不就可以了，其實timeit中還有更有效的辦法：repeat函式

# -*-coding:utf-8-*-
# AUTHOR:tyltr
# TIME :2018/10/11

import timeit


# 待測試的函式
def add():
    return sum(range(111))


# stmt 需要測試的函式或語句，字串形式
# setup 執行的環境，本例子中表示 if __name__ == '__main__':
# number 被測試的函式或語句，執行的次數，本例表示執行100000次add()。省缺則預設是10000次
# repeat 測試做100次
# 綜上：此函式表示 測試 在if __name__ == '__main__'的條件下，執行100000次add()消耗的時間，並把這個測試做100次,並求出平均值

t = timeit.repeat(stmt="add()", setup="from __main__ import add", number=100000, repeat=100)
print(t)
print(sum(t) / len(t))
 

用法已經說完了！下面附的timeit模組的原始碼。有興趣的話，可以看一下。

#! /usr/bin/env python3

"""Tool for measuring execution time of small code snippets.

This module avoids a number of common traps for measuring execution
times.  See also Tim Peters' introduction to the Algorithms chapter in
the Python Cookbook, published by O'Reilly.

Library usage: see the Timer class.

Command line usage:
    python timeit.py [-n N] [-r N] [-s S] [-t] [-c] [-p] [-h] [--] [statement]

Options:
  -n/--number N: how many times to execute 'statement' (default: see below)
  -r/--repeat N: how many times to repeat the timer (default 3)
  -s/--setup S: statement to be executed once initially (default 'pass').
                Execution time of this setup statement is NOT timed.
  -p/--process: use time.process_time() (default is time.perf_counter())
  -t/--time: use time.time() (deprecated)
  -c/--clock: use time.clock() (deprecated)
  -v/--verbose: print raw timing results; repeat for more digits precision
  -u/--unit: set the output time unit (usec, msec, or sec)
  -h/--help: print this usage message and exit
  --: separate options from statement, use when statement starts with -
  statement: statement to be timed (default 'pass')

A multi-line statement may be given by specifying each line as a
separate argument; indented lines are possible by enclosing an
argument in quotes and using leading spaces.  Multiple -s options are
treated similarly.

If -n is not given, a suitable number of loops is calculated by trying
successive powers of 10 until the total time is at least 0.2 seconds.

Note: there is a certain baseline overhead associated with executing a
pass statement.  It differs between versions.  The code here doesn't try
to hide it, but you should be aware of it.  The baseline overhead can be
measured by invoking the program without arguments.

Classes:

    Timer

Functions:

    timeit(string, string) -> float
    repeat(string, string) -> list
    default_timer() -> float

"""

import gc
import sys
import time
import itertools

__all__ = ["Timer", "timeit", "repeat", "default_timer"]

dummy_src_name = "<timeit-src>"
default_number = 1000000
default_repeat = 3
default_timer = time.perf_counter

_globals = globals

# Don't change the indentation of the template; the reindent() calls
# in Timer.__init__() depend on setup being indented 4 spaces and stmt
# being indented 8 spaces.
template = """
def inner(_it, _timer{init}):
    {setup}
    _t0 = _timer()
    for _i in _it:
        {stmt}
    _t1 = _timer()
    return _t1 - _t0
"""

def reindent(src, indent):
    """Helper to reindent a multi-line statement."""
    return src.replace("\n", "\n" + " "*indent)

class Timer:
    """Class for timing execution speed of small code snippets.

    The constructor takes a statement to be timed, an additional
    statement used for setup, and a timer function.  Both statements
    default to 'pass'; the timer function is platform-dependent (see
    module doc string).  If 'globals' is specified, the code will be
    executed within that namespace (as opposed to inside timeit's
    namespace).

    To measure the execution time of the first statement, use the
    timeit() method.  The repeat() method is a convenience to call
    timeit() multiple times and return a list of results.

    The statements may contain newlines, as long as they don't contain
    multi-line string literals.
    """

    def __init__(self, stmt="pass", setup="pass", timer=default_timer,
                 globals=None):
        """Constructor.  See class doc string."""
        self.timer = timer
        local_ns = {}
        global_ns = _globals() if globals is None else globals
        init = ''
        if isinstance(setup, str):
            # Check that the code can be compiled outside a function
            compile(setup, dummy_src_name, "exec")
            stmtprefix = setup + '\n'
            setup = reindent(setup, 4)
        elif callable(setup):
            local_ns['_setup'] = setup
            init += ', _setup=_setup'
            stmtprefix = ''
            setup = '_setup()'
        else:
            raise ValueError("setup is neither a string nor callable")
        if isinstance(stmt, str):
            # Check that the code can be compiled outside a function
            compile(stmtprefix + stmt, dummy_src_name, "exec")
            stmt = reindent(stmt, 8)
        elif callable(stmt):
            local_ns['_stmt'] = stmt
            init += ', _stmt=_stmt'
            stmt = '_stmt()'
        else:
            raise ValueError("stmt is neither a string nor callable")
        src = template.format(stmt=stmt, setup=setup, init=init)
        self.src = src  # Save for traceback display
        code = compile(src, dummy_src_name, "exec")
        exec(code, global_ns, local_ns)
        self.inner = local_ns["inner"]

    def print_exc(self, file=None):
        """Helper to print a traceback from the timed code.

        Typical use:

            t = Timer(...)       # outside the try/except
            try:
                t.timeit(...)    # or t.repeat(...)
            except:
                t.print_exc()

        The advantage over the standard traceback is that source lines
        in the compiled template will be displayed.

        The optional file argument directs where the traceback is
        sent; it defaults to sys.stderr.
        """
        import linecache, traceback
        if self.src is not None:
            linecache.cache[dummy_src_name] = (len(self.src),
                                               None,
                                               self.src.split("\n"),
                                               dummy_src_name)
        # else the source is already stored somewhere else

        traceback.print_exc(file=file)

    def timeit(self, number=default_number):
        """Time 'number' executions of the main statement.

        To be precise, this executes the setup statement once, and
        then returns the time it takes to execute the main statement
        a number of times, as a float measured in seconds.  The
        argument is the number of times through the loop, defaulting
        to one million.  The main statement, the setup statement and
        the timer function to be used are passed to the constructor.
        """
        it = itertools.repeat(None, number)
        gcold = gc.isenabled()
        gc.disable()
        try:
            timing = self.inner(it, self.timer)
        finally:
            if gcold:
                gc.enable()
        return timing

    def repeat(self, repeat=default_repeat, number=default_number):
        """Call timeit() a few times.

        This is a convenience function that calls the timeit()
        repeatedly, returning a list of results.  The first argument
        specifies how many times to call timeit(), defaulting to 3;
        the second argument specifies the timer argument, defaulting
        to one million.

        Note: it's tempting to calculate mean and standard deviation
        from the result vector and report these.  However, this is not
        very useful.  In a typical case, the lowest value gives a
        lower bound for how fast your machine can run the given code
        snippet; higher values in the result vector are typically not
        caused by variability in Python's speed, but by other
        processes interfering with your timing accuracy.  So the min()
        of the result is probably the only number you should be
        interested in.  After that, you should look at the entire
        vector and apply common sense rather than statistics.
        """
        r = []
        for i in range(repeat):
            t = self.timeit(number)
            r.append(t)
        return r

def timeit(stmt="pass", setup="pass", timer=default_timer,
           number=default_number, globals=None):
    """Convenience function to create Timer object and call timeit method."""
    return Timer(stmt, setup, timer, globals).timeit(number)

def repeat(stmt="pass", setup="pass", timer=default_timer,
           repeat=default_repeat, number=default_number, globals=None):
    """Convenience function to create Timer object and call repeat method."""
    return Timer(stmt, setup, timer, globals).repeat(repeat, number)

def main(args=None, *, _wrap_timer=None):
    """Main program, used when run as a script.

    The optional 'args' argument specifies the command line to be parsed,
    defaulting to sys.argv[1:].

    The return value is an exit code to be passed to sys.exit(); it
    may be None to indicate success.

    When an exception happens during timing, a traceback is printed to
    stderr and the return value is 1.  Exceptions at other times
    (including the template compilation) are not caught.

    '_wrap_timer' is an internal interface used for unit testing.  If it
    is not None, it must be a callable that accepts a timer function
    and returns another timer function (used for unit testing).
    """
    if args is None:
        args = sys.argv[1:]
    import getopt
    try:
        opts, args = getopt.getopt(args, "n:u:s:r:tcpvh",
                                   ["number=", "setup=", "repeat=",
                                    "time", "clock", "process",
                                    "verbose", "unit=", "help"])
    except getopt.error as err:
        print(err)
        print("use -h/--help for command line help")
        return 2
    timer = default_timer
    stmt = "\n".join(args) or "pass"
    number = 0 # auto-determine
    setup = []
    repeat = default_repeat
    verbose = 0
    time_unit = None
    units = {"usec": 1, "msec": 1e3, "sec": 1e6}
    precision = 3
    for o, a in opts:
        if o in ("-n", "--number"):
            number = int(a)
        if o in ("-s", "--setup"):
            setup.append(a)
        if o in ("-u", "--unit"):
            if a in units:
                time_unit = a
            else:
                print("Unrecognized unit. Please select usec, msec, or sec.",
                    file=sys.stderr)
                return 2
        if o in ("-r", "--repeat"):
            repeat = int(a)
            if repeat <= 0:
                repeat = 1
        if o in ("-t", "--time"):
            timer = time.time
        if o in ("-c", "--clock"):
            timer = time.clock
        if o in ("-p", "--process"):
            timer = time.process_time
        if o in ("-v", "--verbose"):
            if verbose:
                precision += 1
            verbose += 1
        if o in ("-h", "--help"):
            print(__doc__, end=' ')
            return 0
    setup = "\n".join(setup) or "pass"
    # Include the current directory, so that local imports work (sys.path
    # contains the directory of this script, rather than the current
    # directory)
    import os
    sys.path.insert(0, os.curdir)
    if _wrap_timer is not None:
        timer = _wrap_timer(timer)
    t = Timer(stmt, setup, timer)
    if number == 0:
        # determine number so that 0.2 <= total time < 2.0
        for i in range(1, 10):
            number = 10**i
            try:
                x = t.timeit(number)
            except:
                t.print_exc()
                return 1
            if verbose:
                print("%d loops -> %.*g secs" % (number, precision, x))
            if x >= 0.2:
                break
    try:
        r = t.repeat(repeat, number)
    except:
        t.print_exc()
        return 1
    best = min(r)
    if verbose:
        print("raw times:", " ".join(["%.*g" % (precision, x) for x in r]))
    print("%d loops," % number, end=' ')
    usec = best * 1e6 / number
    if time_unit is not None:
        print("best of %d: %.*g %s per loop" % (repeat, precision,
                                             usec/units[time_unit], time_unit))
    else:
        if usec < 1000:
            print("best of %d: %.*g usec per loop" % (repeat, precision, usec))
        else:
            msec = usec / 1000
            if msec < 1000:
                print("best of %d: %.*g msec per loop" % (repeat,
                                                          precision, msec))
            else:
                sec = msec / 1000
                print("best of %d: %.*g sec per loop" % (repeat,
                                                         precision, sec))
    return None

if __name__ == "__main__":
    sys.exit(main())