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(from 10) and in main() (from 1). Add a -v option that shows the raw times. Repeating it cranks up the display precision. Always use the "best of N" form of output.
265 lines
9.4 KiB
Python
265 lines
9.4 KiB
Python
"""Tool for measuring execution time of small code snippets.
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This module avoids a number of common traps for measuring execution
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times. See also Tim Peters' introduction to the Algorithms chapter in
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the Python Cookbook, published by O'Reilly.
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Library usage: see the Timer class.
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Command line usage:
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python timeit.py [-n N] [-r N] [-s S] [-t] [-c] [-h] [statement]
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Options:
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-n/--number N: how many times to execute 'statement' (default: see below)
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-r/--repeat N: how many times to repeat the timer (default 3)
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-s/--setup S: statement to be executed once initially (default 'pass')
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-t/--time: use time.time() (default on Unix)
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-c/--clock: use time.clock() (default on Windows)
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-v/--verbose: print raw timing results; repeat for more digits precision
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-h/--help: print this usage message and exit
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statement: statement to be timed (default 'pass')
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A multi-line statement may be given by specifying each line as a
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separate argument; indented lines are possible by enclosing an
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argument in quotes and using leading spaces. Multiple -s options are
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treated similarly.
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If -n is not given, a suitable number of loops is calculated by trying
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successive powers of 10 until the total time is at least 0.2 seconds.
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The difference in default timer function is because on Windows,
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clock() has microsecond granularity but time()'s granularity is 1/60th
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of a second; on Unix, clock() has 1/100th of a second granularity and
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time() is much more precise. On either platform, the default timer
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functions measures wall clock time, not the CPU time. This means that
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other processes running on the same computer may interfere with the
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timing. The best thing to do when accurate timing is necessary is to
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repeat the timing a few times and use the best time. The -r option is
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good for this; the default of 3 repetitions is probably enough in most
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cases. On Unix, you can use clock() to measure CPU time.
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Note: there is a certain baseline overhead associated with executing a
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pass statement. The code here doesn't try to hide it, but you should
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be aware of it. The baseline overhead can be measured by invoking the
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program without arguments.
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The baseline overhead differs between Python versions! Also, to
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fairly compare older Python versions to Python 2.3, you may want to
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use python -O for the older versions to avoid timing SET_LINENO
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instructions.
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"""
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import sys
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import math
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import time
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try:
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import itertools
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except ImportError:
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# Must be an older Python version (see timeit() below)
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itertools = None
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__all__ = ["Timer"]
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dummy_src_name = "<timeit-src>"
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default_number = 1000000
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default_repeat = 3
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if sys.platform == "win32":
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# On Windows, the best timer is time.clock()
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default_timer = time.clock
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else:
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# On most other platforms the best timer is time.time()
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default_timer = time.time
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# Don't change the indentation of the template; the reindent() calls
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# in Timer.__init__() depend on setup being indented 4 spaces and stmt
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# being indented 8 spaces.
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template = """
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def inner(_seq, _timer):
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%(setup)s
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_t0 = _timer()
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for _i in _seq:
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%(stmt)s
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_t1 = _timer()
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return _t1 - _t0
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"""
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def reindent(src, indent):
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"""Helper to reindent a multi-line statement."""
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return src.replace("\n", "\n" + " "*indent)
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class Timer:
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"""Class for timing execution speed of small code snippets.
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The constructor takes a statement to be timed, an additional
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statement used for setup, and a timer function. Both statements
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default to 'pass'; the timer function is platform-dependent (see
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module doc string).
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To measure the execution time of the first statement, use the
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timeit() method. The repeat() method is a convenience to call
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timeit() multiple times and return a list of results.
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The statements may contain newlines, as long as they don't contain
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multi-line string literals.
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"""
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def __init__(self, stmt="pass", setup="pass", timer=default_timer):
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"""Constructor. See class doc string."""
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self.timer = timer
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stmt = reindent(stmt, 8)
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setup = reindent(setup, 4)
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src = template % {'stmt': stmt, 'setup': setup}
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self.src = src # Save for traceback display
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code = compile(src, dummy_src_name, "exec")
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ns = {}
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exec code in globals(), ns
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self.inner = ns["inner"]
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def print_exc(self, file=None):
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"""Helper to print a traceback from the timed code.
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Typical use:
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t = Timer(...) # outside the try/except
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try:
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t.timeit(...) # or t.repeat(...)
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except:
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t.print_exc()
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The advantage over the standard traceback is that source lines
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in the compiled template will be displayed.
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The optional file argument directs where the traceback is
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sent; it defaults to sys.stderr.
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"""
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import linecache, traceback
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linecache.cache[dummy_src_name] = (len(self.src),
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None,
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self.src.split("\n"),
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dummy_src_name)
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traceback.print_exc(file=file)
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def timeit(self, number=default_number):
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"""Time 'number' executions of the main statement.
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To be precise, this executes the setup statement once, and
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then returns the time it takes to execute the main statement
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a number of times, as a float measured in seconds. The
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argument is the number of times through the loop, defaulting
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to one million. The main statement, the setup statement and
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the timer function to be used are passed to the constructor.
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"""
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if itertools:
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seq = itertools.repeat(None, number)
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else:
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seq = [None] * number
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return self.inner(seq, self.timer)
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def repeat(self, repeat=default_repeat, number=default_number):
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"""Call timer() a few times.
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This is a convenience function that calls the timer()
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repeatedly, returning a list of results. The first argument
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specifies how many times to call timer(), defaulting to 3;
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the second argument specifies the timer argument, defaulting
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to one million.
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Note: it's tempting to calculate mean and standard deviation
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from the result vector and report these. However, this is not
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very useful. In a typical case, the lowest value gives a
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lower bound for how fast your machine can run the given code
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snippet; higher values in the result vector are typically not
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caused by variability in Python's speed, but by other
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processes interfering with your timing accuracy. So the min()
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of the result is probably the only number you should be
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interested in. After that, you should look at the entire
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vector and apply common sense rather than statistics.
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"""
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r = []
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for i in range(repeat):
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t = self.timeit(number)
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r.append(t)
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return r
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def main(args=None):
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"""Main program, used when run as a script.
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The optional argument specifies the command line to be parsed,
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defaulting to sys.argv[1:].
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The return value is an exit code to be passed to sys.exit(); it
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may be None to indicate success.
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When an exception happens during timing, a traceback is printed to
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stderr and the return value is 1. Exceptions at other times
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(including the template compilation) are not caught.
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"""
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if args is None:
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args = sys.argv[1:]
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import getopt
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try:
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opts, args = getopt.getopt(args, "n:s:r:tcvh",
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["number=", "setup=", "repeat=",
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"time", "clock", "verbose", "help"])
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except getopt.error, err:
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print err
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print "use -h/--help for command line help"
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return 2
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timer = default_timer
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stmt = "\n".join(args) or "pass"
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number = 0 # auto-determine
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setup = []
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repeat = default_repeat
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verbose = 0
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precision = 3
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for o, a in opts:
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if o in ("-n", "--number"):
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number = int(a)
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if o in ("-s", "--setup"):
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setup.append(a)
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if o in ("-r", "--repeat"):
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repeat = int(a)
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if repeat <= 0:
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repeat = 1
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if o in ("-t", "--time"):
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timer = time.time
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if o in ("-c", "--clock"):
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timer = time.clock
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if o in ("-v", "--verbose"):
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if verbose:
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precision += 1
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verbose += 1
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if o in ("-h", "--help"):
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print __doc__,
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return 0
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setup = "\n".join(setup) or "pass"
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t = Timer(stmt, setup, timer)
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if number == 0:
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# determine number so that 0.2 <= total time < 2.0
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for i in range(1, 10):
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number = 10**i
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try:
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x = t.timeit(number)
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except:
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t.print_exc()
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return 1
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if verbose:
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print "%d loops -> %.*g secs" % (number, precision, x)
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if x >= 0.2:
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break
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try:
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r = t.repeat(repeat, number)
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except:
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t.print_exc()
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return 1
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best = min(r)
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if verbose:
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print "raw times:", " ".join(["%.*g" % (precision, x) for x in r])
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print "%d loops," % number,
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usec = best * 1e6 / number
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print "best of %d: %.*g usec per loop" % (repeat, precision, usec)
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return None
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if __name__ == "__main__":
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sys.exit(main())
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