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377 lines
13 KiB
377 lines
13 KiB
3 years ago
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#! /usr/bin/env python3
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"""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] [-p] [-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 5)
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-s/--setup S: statement to be executed once initially (default 'pass').
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Execution time of this setup statement is NOT timed.
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-p/--process: use time.process_time() (default is time.perf_counter())
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-v/--verbose: print raw timing results; repeat for more digits precision
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-u/--unit: set the output time unit (nsec, usec, msec, or sec)
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-h/--help: print this usage message and exit
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--: separate options from statement, use when statement starts with -
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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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increasing numbers from the sequence 1, 2, 5, 10, 20, 50, ... until the
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total time is at least 0.2 seconds.
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Note: there is a certain baseline overhead associated with executing a
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pass statement. It differs between versions. The code here doesn't try
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to hide it, but you should be aware of it. The baseline overhead can be
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measured by invoking the program without arguments.
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Classes:
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Timer
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Functions:
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timeit(string, string) -> float
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repeat(string, string) -> list
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default_timer() -> float
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"""
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import gc
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import sys
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import time
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import itertools
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__all__ = ["Timer", "timeit", "repeat", "default_timer"]
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dummy_src_name = "<timeit-src>"
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default_number = 1000000
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default_repeat = 5
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default_timer = time.perf_counter
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_globals = globals
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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(_it, _timer{init}):
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{setup}
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_t0 = _timer()
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for _i in _it:
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{stmt}
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pass
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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). If 'globals' is specified, the code will be
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executed within that namespace (as opposed to inside timeit's
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namespace).
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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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globals=None):
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"""Constructor. See class doc string."""
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self.timer = timer
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local_ns = {}
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global_ns = _globals() if globals is None else globals
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init = ''
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if isinstance(setup, str):
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# Check that the code can be compiled outside a function
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compile(setup, dummy_src_name, "exec")
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stmtprefix = setup + '\n'
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setup = reindent(setup, 4)
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elif callable(setup):
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local_ns['_setup'] = setup
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init += ', _setup=_setup'
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stmtprefix = ''
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setup = '_setup()'
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else:
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raise ValueError("setup is neither a string nor callable")
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if isinstance(stmt, str):
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# Check that the code can be compiled outside a function
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compile(stmtprefix + stmt, dummy_src_name, "exec")
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stmt = reindent(stmt, 8)
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elif callable(stmt):
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local_ns['_stmt'] = stmt
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init += ', _stmt=_stmt'
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stmt = '_stmt()'
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else:
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raise ValueError("stmt is neither a string nor callable")
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src = template.format(stmt=stmt, setup=setup, init=init)
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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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exec(code, global_ns, local_ns)
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self.inner = local_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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if self.src is not None:
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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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# else the source is already stored somewhere else
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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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it = itertools.repeat(None, number)
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gcold = gc.isenabled()
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gc.disable()
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try:
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timing = self.inner(it, self.timer)
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finally:
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if gcold:
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gc.enable()
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return timing
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def repeat(self, repeat=default_repeat, number=default_number):
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"""Call timeit() a few times.
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This is a convenience function that calls the timeit()
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repeatedly, returning a list of results. The first argument
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specifies how many times to call timeit(), defaulting to 5;
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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 autorange(self, callback=None):
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"""Return the number of loops and time taken so that total time >= 0.2.
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Calls the timeit method with increasing numbers from the sequence
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1, 2, 5, 10, 20, 50, ... until the time taken is at least 0.2
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second. Returns (number, time_taken).
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If *callback* is given and is not None, it will be called after
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each trial with two arguments: ``callback(number, time_taken)``.
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"""
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i = 1
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while True:
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for j in 1, 2, 5:
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number = i * j
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time_taken = self.timeit(number)
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if callback:
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callback(number, time_taken)
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if time_taken >= 0.2:
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return (number, time_taken)
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i *= 10
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def timeit(stmt="pass", setup="pass", timer=default_timer,
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number=default_number, globals=None):
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"""Convenience function to create Timer object and call timeit method."""
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return Timer(stmt, setup, timer, globals).timeit(number)
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def repeat(stmt="pass", setup="pass", timer=default_timer,
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repeat=default_repeat, number=default_number, globals=None):
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"""Convenience function to create Timer object and call repeat method."""
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return Timer(stmt, setup, timer, globals).repeat(repeat, number)
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def main(args=None, *, _wrap_timer=None):
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"""Main program, used when run as a script.
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The optional 'args' 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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'_wrap_timer' is an internal interface used for unit testing. If it
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is not None, it must be a callable that accepts a timer function
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and returns another timer function (used for unit testing).
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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:u:s:r:tcpvh",
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["number=", "setup=", "repeat=",
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"time", "clock", "process",
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"verbose", "unit=", "help"])
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except getopt.error as 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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time_unit = None
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units = {"nsec": 1e-9, "usec": 1e-6, "msec": 1e-3, "sec": 1.0}
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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 ("-u", "--unit"):
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if a in units:
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time_unit = a
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else:
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print("Unrecognized unit. Please select nsec, usec, msec, or sec.",
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file=sys.stderr)
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return 2
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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 ("-p", "--process"):
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timer = time.process_time
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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__, end=' ')
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return 0
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setup = "\n".join(setup) or "pass"
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# Include the current directory, so that local imports work (sys.path
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# contains the directory of this script, rather than the current
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# directory)
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import os
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sys.path.insert(0, os.curdir)
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if _wrap_timer is not None:
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timer = _wrap_timer(timer)
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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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callback = None
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if verbose:
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def callback(number, time_taken):
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msg = "{num} loop{s} -> {secs:.{prec}g} secs"
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plural = (number != 1)
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print(msg.format(num=number, s='s' if plural else '',
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secs=time_taken, prec=precision))
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try:
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number, _ = t.autorange(callback)
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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()
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try:
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raw_timings = 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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def format_time(dt):
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unit = time_unit
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if unit is not None:
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scale = units[unit]
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else:
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scales = [(scale, unit) for unit, scale in units.items()]
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scales.sort(reverse=True)
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for scale, unit in scales:
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if dt >= scale:
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break
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return "%.*g %s" % (precision, dt / scale, unit)
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if verbose:
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print("raw times: %s" % ", ".join(map(format_time, raw_timings)))
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print()
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timings = [dt / number for dt in raw_timings]
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best = min(timings)
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print("%d loop%s, best of %d: %s per loop"
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% (number, 's' if number != 1 else '',
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repeat, format_time(best)))
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best = min(timings)
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worst = max(timings)
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if worst >= best * 4:
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import warnings
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warnings.warn_explicit("The test results are likely unreliable. "
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"The worst time (%s) was more than four times "
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"slower than the best time (%s)."
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% (format_time(worst), format_time(best)),
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UserWarning, '', 0)
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return None
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if __name__ == "__main__":
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sys.exit(main())
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