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@sgryjp sgryjp/stopwatch.py
Created Dec 5, 2018

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Stopwatch to measure code execution time inside a `with` statement.
import time
import statistics
class Stopwatch(object):
"""Stopwatch to measure code execution time.
A Stopwatch object measures execution time of code inside one or more
`with` statements. Using a single object multiple times let it store
timing data every time.
If a callable was given to `print_fn` parameter, it will be called with
stringified Stopwatch instance (i.e.: `str(stopwatch)`) on each exit from
a `with` statement. Typical suitable function would be `print` or
`logging.debug`.
Example
-------
>>> sw = Stopwatch()
>>> for _ in range(3):
... with sw:
... sum(n for n in range(1_000_000)
>>> str(sw)
607 ms ± 8.82 ms per laps (mean ± std. dev. of 3 laps)
>>> sw.mean(), sw.stdev()
0.6070484847993166 0.00882254275134833
>>> sw.intervals
[0.6147285757252803, 0.6090049394119035, 0.5974119392607662]
"""
def __init__(self, print_fn=None):
self._t0 = 0.
self.intervals = []
self.print_fn = print_fn
def __enter__(self):
self._t0 = time.perf_counter()
def __exit__(self, exc_type, exc_value, traceback):
self.intervals.append(time.perf_counter() - self._t0)
if self.print_fn:
self.print_fn(str(self))
def __str__(self):
laps = len(self.intervals)
mean, stdev = self.mean(), self.stdev()
if mean >= 1:
k = 1
unit = 's'
elif mean >= 1e-3:
k = 10**3
unit = 'ms'
elif mean >= 1e-6:
k = 10**6
unit = 'μs'
else:
k = 10**9
unit = 'ns'
mean *= k
stdev *= k
return ('{mean:.3g} {unit} ± {stdev:.3g} {unit} per laps'
' (mean ± std. dev. of {laps} laps)'.format(**vars()))
def mean(self, unit='s'):
"""Calculate mean of the intervals.
Parameters
----------
unit : str [optional]
Time unit. Allowed values are: 'ms', 'us', 'ns' and 's' (default).
Returns
-------
mean : float
Mean of the measured intervals, or NaN if no intervals are
measured.
"""
try:
t = statistics.mean(self.intervals)
return t * {'ms': 10**3, 'us': 10**6, 'ns': 10**9}.get(unit, 1)
except statistics.StatisticsError:
return float('nan')
def stdev(self, unit='s'):
"""Calculate standard deviation of the intervals.
Parameters
----------
unit : str [optional]
Time unit. Allowed values are: 'ms', 'us', 'ns' and 's' (default).
Returns
-------
stdev : float
Standard deviation of the measured intervals, or NaN if number of
intervals are less than two.
"""
try:
t = statistics.stdev(self.intervals)
return t * {'ms': 10**3, 'us': 10**6, 'ns': 10**9}.get(unit, 1)
except statistics.StatisticsError:
return float('nan')
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