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Diffstat (limited to 'bench/timeit.py')
| -rw-r--r-- | bench/timeit.py | 297 |
1 files changed, 297 insertions, 0 deletions
diff --git a/bench/timeit.py b/bench/timeit.py new file mode 100644 index 00000000..d5e33bb1 --- /dev/null +++ b/bench/timeit.py @@ -0,0 +1,297 @@ +#! /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. +""" + +try: + import gc +except ImportError: + class _fake_gc: + def isenabled(self): + return None + def enable(self): + pass + def disable(self): + pass + gc = _fake_gc() +import sys +import time +try: + import itertools +except ImportError: + # Must be an older Python version (see timeit() below) + itertools = None + +import string + +__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 string.replace(src, "\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 = string.join(args, "\n") 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 = precision + 1 + verbose = precision + 1 + if o in ("-h", "--help"): + print __doc__, + return 0 + setup = string.join(setup, "\n") 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:", string.join(map(lambda x, p=precision: "%.*g" % (p, x), 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()) |