#! /usr/bin/env python

"""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] [-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')

  -t/--time: use time.time() (default on Unix)

  -c/--clock: use time.clock() (default on Windows)

  -v/--verbose: print raw timing results; repeat for more digits precision

  -h/--help: print this usage message and exit

  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.

The difference in default timer function is because on Windows,

clock() has microsecond granularity but time()'s granularity is 1/60th

of a second; on Unix, clock() has 1/100th of a second granularity and

time() is much more precise.  On either platform, the default timer

functions measure wall clock time, not the CPU time.  This means that

other processes running on the same computer may interfere with the

timing.  The best thing to do when accurate timing is necessary is to

repeat the timing a few times and use the best time.  The -r option is

good for this; the default of 3 repetitions is probably enough in most

cases.  On Unix, you can use clock() to measure CPU time.

Note: there is a certain baseline overhead associated with executing a

pass statement.  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.

The baseline overhead differs between Python versions!  Also, to

fairly compare older Python versions to Python 2.3, you may want to

use python -O for the older versions to avoid timing SET_LINENO

instructions.

"""

import gc

import sys

import time

try:

    import itertools

except ImportError:

    # Must be an older Python version (see timeit() below)

    itertools = None

__all__ = ["Timer"]

dummy_src_name = "<timeit-src>"

default_number = 1000000

default_repeat = 3

if sys.platform == "win32":

    # On Windows, the best timer is time.clock()

    default_timer = time.clock

else:

    # On most other platforms the best timer is time.time()

    default_timer = time.time

# 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):

    %(setup)s

    _t0 = _timer()

    for _i in _it:

        %(stmt)s

    _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).

    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):

        """Constructor.  See class doc string."""

        self.timer = timer

        stmt = reindent(stmt, 8)

        setup = reindent(setup, 4)

        src = template % {'stmt': stmt, 'setup': setup}

        self.src = src # Save for traceback display

        code = compile(src, dummy_src_name, "exec")

        ns = {}

        exec code in globals(), ns

        self.inner = 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

        linecache.cache[dummy_src_name] = (len(self.src),

                                           None,

                                           self.src.split("\n"),

                                           dummy_src_name)

        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.

        """

        if itertools:

            it = itertools.repeat(None, number)

        else:

            it = [None] * number

        gcold = gc.isenabled()

        gc.disable()

        timing = self.inner(it, self.timer)

        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 main(args=None):

    """Main program, used when run as a script.

    The optional 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.

    """

    if args is None:

        args = sys.argv[1:]

    import getopt

    try:

        opts, args = getopt.getopt(args, "n:s:r:tcvh",

                                   ["number=", "setup=", "repeat=",

                                    "time", "clock", "verbose", "help"])

    except getopt.error, 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

    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 ("-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 ("-v", "--verbose"):

            if verbose:

                precision += 1

            verbose += 1

        if o in ("-h", "--help"):

            print __doc__,

            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)

    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,

    usec = best * 1e6 / number

    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())