In this article, we will learn to calculate the time taken by a program to execute in Python. We will use some built-in functions with some custom codes as well. Let’s first have a quick look over how the program’s execution affects the time in Python.
Programmers must have often suffered from «Time Limit Exceeded» error while building program scripts. In order to resolve this issue, we must optimize our programs to perform better. For that, we might need to know how much time the program is taking for its execution. Let us discuss different functions supported by Python to calculate the running time of a program in python.
The time of a Python program’s execution measure could be inconsistent depending on the following factors:
- The same program can be evaluated using different algorithms
- Running time varies between algorithms
- Running time varies between implementations
- Running time varies between computers
- Running time is not predictable based on small inputs
Calculate Execution Time using time() Function
We calculate the execution time of the program using time.time()
function. It imports the time
module which can be used to get the current time. The below example stores the starting time before the for loop executes, then it stores the ending time after the print line executes. The difference between the ending time and starting time will be the running time of the program. time.time()
function is best used on *nix.
import time
#starting time
start = time.time()
for i in range(3):
print("Hello")
# end time
end = time.time()
# total time taken
print("Execution time of the program is- ", end-start)
Hello
Hello
Hello
Execution time of the program is- 1.430511474609375e-05
Calculate execution time using timeit() function
We calculate the execution time of the program using timeit()
function. It imports the timeit
module. The result is the execution time in seconds. This assumes that your program takes at least a tenth of a second to run.
The below example creates a variable and wraps the entire code including imports inside triple quotes. The test code acts as a string. Now, we call the time.timeit()
function. The timeit()
function accepts the test code as an argument, executes it, and records the execution time. The value of the number argument is set to 100 cycles.
import timeit
test_code = """
a = range(100000)
b = []
for i in a:
b.append(i+2)
"""
total_time = timeit.timeit(test_code, number=200)
print("Execution time of the program is-", total_time)
Execution time of the program is- 4.26646219700342
Calculate execution time using time.clock() Function
Another function of the time module to measure the time of a program’s execution is time.clock()
function. time.clock()
measures CPU time on Unix systems, not wall time. This function is mainly used for benchmarking purposes or timing algorithms. time.clock()
may return slightly better accuracy than time.time()
. It returns the processor time, which allows us to calculate only the time used by this process. It is best used on Windows.
import time
t0= time.clock()
print("Hello")
t1 = time.clock() - t0
print("Time elapsed: ", t1 - t0) # CPU seconds elapsed (floating point)
Hello
Time elapsed: -0.02442
Note:
time.clock()
is «Deprecated since version 3.3». The behavior of this function depends on the platform. Instead, we can use perf_counter() or process_time() depending on the requirements or have a well-defined behavior.
time.perf_counter()
— It returns the value (in fractional seconds) of a performance counter, i.e. a clock with the highest available resolution to measure a short duration. It does include time elapsed during sleep and is system-wide.
time.process_time()
— It returns the value (in fractional seconds) of the sum of the system and user CPU time of the current process. It does not include time elapsed during sleep. For example,
start = time.process_time()
... do something
elapsed = (time.process_time() - start)
Calculate execution time using datetime.now() Function
We calculate the elapsed time using datetime.datetime.now()
from the datetime
module available in Python. It does not make the script a multi-line string like in timeit()
. This solution is slower than the timeit()
since calculating the difference in time is included in the execution time. The output is represented as days, hours, minutes, etc
The below example saves the current time before any execution in a variable. Then call datetime.datetime.now()
after the program execution to find the difference between the end and start time of execution.
import datetime
start = datetime.datetime.now()
list1 = [4, 2, 3, 1, 5]
list1.sort()
end = datetime.datetime.now()
print(end-start)
0:00:00.000007
Calculate execution time using %%time
We use %%time
command to calculate the time elapsed by the program. This command is basically for the users who are working on Jupyter Notebook. This will only capture the wall time of a particular cell.
%%time
[ x**2 for x in range(10000)]
Why is timeit() the best way to measure the execution time of Python code?
1. You can also use time.clock()
on Windows and time.time()
on Mac or Linux. However, timeit()
will automatically use either time.clock()
or time.time()
in the background depending on the operating system.
2. timeit()
disables the garbage collector which could otherwise skew the results.
3. timeit()
repeats the test many times to minimize the influence of other tasks running on your operating system.
Conclusion
In this article, we learned to calculate the time of execution of any program by using functions such as time()
, clock()
, timeit()
, %%time
etc. We also discussed the optimization of the python script. We learned about various functions and their uniqueness.
The simplest way in Python:
import time
start_time = time.time()
main()
print("--- %s seconds ---" % (time.time() - start_time))
This assumes that your program takes at least a tenth of second to run.
Prints:
--- 0.764891862869 seconds ---
answered Oct 13, 2009 at 0:00
rogeriopvlrogeriopvl
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In Linux or Unix:
$ time python yourprogram.py
In Windows, see this StackOverflow question: How do I measure execution time of a command on the Windows command line?
For more verbose output,
$ time -v python yourprogram.py
Command being timed: "python3 yourprogram.py"
User time (seconds): 0.08
System time (seconds): 0.02
Percent of CPU this job got: 98%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.10
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 9480
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 1114
Voluntary context switches: 0
Involuntary context switches: 22
Swaps: 0
File system inputs: 0
File system outputs: 0
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0
answered Oct 12, 2009 at 23:59
stevehasteveha
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I put this timing.py
module into my own site-packages
directory, and just insert import timing
at the top of my module:
import atexit
from time import clock
def secondsToStr(t):
return "%d:%02d:%02d.%03d" %
reduce(lambda ll,b : divmod(ll[0],b) + ll[1:],
[(t*1000,),1000,60,60])
line = "="*40
def log(s, elapsed=None):
print line
print secondsToStr(clock()), '-', s
if elapsed:
print "Elapsed time:", elapsed
print line
print
def endlog():
end = clock()
elapsed = end-start
log("End Program", secondsToStr(elapsed))
def now():
return secondsToStr(clock())
start = clock()
atexit.register(endlog)
log("Start Program")
I can also call timing.log
from within my program if there are significant stages within the program I want to show. But just including import timing
will print the start and end times, and overall elapsed time. (Forgive my obscure secondsToStr
function, it just formats a floating point number of seconds to hh:mm:ss.sss form.)
Note: A Python 3 version of the above code can be found here or here.
answered Oct 13, 2009 at 2:08
PaulMcGPaulMcG
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I like the output the datetime
module provides, where time delta objects show days, hours, minutes, etc. as necessary in a human-readable way.
For example:
from datetime import datetime
start_time = datetime.now()
# do your work here
end_time = datetime.now()
print('Duration: {}'.format(end_time - start_time))
Sample output e.g.
Duration: 0:00:08.309267
or
Duration: 1 day, 1:51:24.269711
As J.F. Sebastian mentioned, this approach might encounter some tricky cases with local time, so it’s safer to use:
import time
from datetime import timedelta
start_time = time.monotonic()
end_time = time.monotonic()
print(timedelta(seconds=end_time - start_time))
answered Sep 29, 2014 at 11:55
metakermitmetakermit
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import time
start_time = time.clock()
main()
print(time.clock() - start_time, "seconds")
time.clock()
returns the processor time, which allows us to calculate only the time used by this process (on Unix anyway). The documentation says «in any case, this is the function to use for benchmarking Python or timing algorithms»
Shidouuu
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answered Oct 13, 2009 at 1:25
newacctnewacct
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I really like Paul McGuire’s answer, but I use Python 3. So for those who are interested: here’s a modification of his answer that works with Python 3 on *nix (I imagine, under Windows, that clock()
should be used instead of time()
):
#python3
import atexit
from time import time, strftime, localtime
from datetime import timedelta
def secondsToStr(elapsed=None):
if elapsed is None:
return strftime("%Y-%m-%d %H:%M:%S", localtime())
else:
return str(timedelta(seconds=elapsed))
def log(s, elapsed=None):
line = "="*40
print(line)
print(secondsToStr(), '-', s)
if elapsed:
print("Elapsed time:", elapsed)
print(line)
print()
def endlog():
end = time()
elapsed = end-start
log("End Program", secondsToStr(elapsed))
start = time()
atexit.register(endlog)
log("Start Program")
If you find this useful, you should still up-vote his answer instead of this one, as he did most of the work ;).
Georgy
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answered Sep 10, 2012 at 2:03
NicojoNicojo
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You can use the Python profiler cProfile to measure CPU time and additionally how much time is spent inside each function and how many times each function is called. This is very useful if you want to improve performance of your script without knowing where to start. This answer to another Stack Overflow question is pretty good. It’s always good to have a look in the documentation too.
Here’s an example how to profile a script using cProfile from a command line:
$ python -m cProfile euler048.py
1007 function calls in 0.061 CPU seconds
Ordered by: standard name
ncalls tottime percall cumtime percall filename:lineno(function)
1 0.000 0.000 0.061 0.061 <string>:1(<module>)
1000 0.051 0.000 0.051 0.000 euler048.py:2(<lambda>)
1 0.005 0.005 0.061 0.061 euler048.py:2(<module>)
1 0.000 0.000 0.061 0.061 {execfile}
1 0.002 0.002 0.053 0.053 {map}
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler objects}
1 0.000 0.000 0.000 0.000 {range}
1 0.003 0.003 0.003 0.003 {sum}
answered Jan 2, 2014 at 0:35
jacwahjacwah
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Just use the timeit
module. It works with both Python 2 and Python 3.
import timeit
start = timeit.default_timer()
# All the program statements
stop = timeit.default_timer()
execution_time = stop - start
print("Program Executed in "+str(execution_time)) # It returns time in seconds
It returns in seconds and you can have your execution time. It is simple, but you should write these in thew main function which starts program execution. If you want to get the execution time even when you get an error then take your parameter «Start» to it and calculate there like:
def sample_function(start,**kwargs):
try:
# Your statements
except:
# except statements run when your statements raise an exception
stop = timeit.default_timer()
execution_time = stop - start
print("Program executed in " + str(execution_time))
djamaile
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answered Sep 18, 2017 at 19:08
Ravi KumarRavi Kumar
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time.clock()
Deprecated since version 3.3: The behavior of this function depends
on the platform: use perf_counter() or process_time() instead,
depending on your requirements, to have a well-defined behavior.
time.perf_counter()
Return the value (in fractional seconds) of a performance counter,
i.e. a clock with the highest available resolution to measure a short
duration. It does include time elapsed during sleep and is
system-wide.
time.process_time()
Return the value (in fractional seconds) of the sum of the system and
user CPU time of the current process. It does not include time elapsed
during sleep.
start = time.process_time()
... do something
elapsed = (time.process_time() - start)
answered May 18, 2016 at 3:49
YasYas
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1
time.clock
has been deprecated in Python 3.3 and will be removed from Python 3.8: use time.perf_counter
or time.process_time
instead
import time
start_time = time.perf_counter ()
for x in range(1, 100):
print(x)
end_time = time.perf_counter ()
print(end_time - start_time, "seconds")
Suraj Rao
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answered Jun 20, 2021 at 9:11
1
For the data folks using Jupyter Notebook
In a cell, you can use Jupyter’s %%time
magic command to measure the execution time:
%%time
[ x**2 for x in range(10000)]
Output
CPU times: user 4.54 ms, sys: 0 ns, total: 4.54 ms
Wall time: 4.12 ms
This will only capture the execution time of a particular cell. If you’d like to capture the execution time of the whole notebook (i.e. program), you can create a new notebook in the same directory and in the new notebook execute all cells:
Suppose the notebook above is called example_notebook.ipynb
. In a new notebook within the same directory:
# Convert your notebook to a .py script:
!jupyter nbconvert --to script example_notebook.ipynb
# Run the example_notebook with -t flag for time
%run -t example_notebook
Output
IPython CPU timings (estimated):
User : 0.00 s.
System : 0.00 s.
Wall time: 0.00 s.
answered Jul 28, 2018 at 16:48
MattMatt
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The following snippet prints elapsed time in a nice human readable <HH:MM:SS>
format.
import time
from datetime import timedelta
start_time = time.time()
#
# Perform lots of computations.
#
elapsed_time_secs = time.time() - start_time
msg = "Execution took: %s secs (Wall clock time)" % timedelta(seconds=round(elapsed_time_secs))
print(msg)
answered Jul 1, 2016 at 22:24
SandeepSandeep
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1
Similar to the response from @rogeriopvl I added a slight modification to convert to hour minute seconds using the same library for long running jobs.
import time
start_time = time.time()
main()
seconds = time.time() - start_time
print('Time Taken:', time.strftime("%H:%M:%S",time.gmtime(seconds)))
Sample Output
Time Taken: 00:00:08
answered Mar 12, 2020 at 5:27
user 923227user 923227
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1
For functions, I suggest using this simple decorator I created.
def timeit(method):
def timed(*args, **kwargs):
ts = time.time()
result = method(*args, **kwargs)
te = time.time()
if 'log_time' in kwargs:
name = kwargs.get('log_name', method.__name__.upper())
kwargs['log_time'][name] = int((te - ts) * 1000)
else:
print('%r %2.22f ms' % (method.__name__, (te - ts) * 1000))
return result
return timed
@timeit
def foo():
do_some_work()
# foo()
# 'foo' 0.000953 ms
answered Oct 29, 2020 at 10:24
Nikita TonkoskurNikita Tonkoskur
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from time import time
start_time = time()
...
end_time = time()
time_taken = end_time - start_time # time_taken is in seconds
hours, rest = divmod(time_taken,3600)
minutes, seconds = divmod(rest, 60)
The6thSense
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answered Apr 6, 2016 at 7:45
Qina YanQina Yan
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I’ve looked at the timeit module, but it seems it’s only for small snippets of code. I want to time the whole program.
$ python -mtimeit -n1 -r1 -t -s "from your_module import main" "main()"
It runs your_module.main()
function one time and print the elapsed time using time.time()
function as a timer.
To emulate /usr/bin/time
in Python see Python subprocess with /usr/bin/time: how to capture timing info but ignore all other output?.
To measure CPU time (e.g., don’t include time during time.sleep()
) for each function, you could use profile
module (cProfile
on Python 2):
$ python3 -mprofile your_module.py
You could pass -p
to timeit
command above if you want to use the same timer as profile
module uses.
See How can you profile a Python script?
answered Mar 3, 2015 at 9:04
jfsjfs
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I was having the same problem in many places, so I created a convenience package horology
. You can install it with pip install horology
and then do it in the elegant way:
from horology import Timing
with Timing(name='Important calculations: '):
prepare()
do_your_stuff()
finish_sth()
will output:
Important calculations: 12.43 ms
Or even simpler (if you have one function):
from horology import timed
@timed
def main():
...
will output:
main: 7.12 h
It takes care of units and rounding. It works with python 3.6 or newer.
answered Dec 7, 2019 at 22:05
hanshans
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I liked Paul McGuire’s answer too and came up with a context manager form which suited my needs more.
import datetime as dt
import timeit
class TimingManager(object):
"""Context Manager used with the statement 'with' to time some execution.
Example:
with TimingManager() as t:
# Code to time
"""
clock = timeit.default_timer
def __enter__(self):
"""
"""
self.start = self.clock()
self.log('n=> Start Timing: {}')
return self
def __exit__(self, exc_type, exc_val, exc_tb):
"""
"""
self.endlog()
return False
def log(self, s, elapsed=None):
"""Log current time and elapsed time if present.
:param s: Text to display, use '{}' to format the text with
the current time.
:param elapsed: Elapsed time to display. Dafault: None, no display.
"""
print s.format(self._secondsToStr(self.clock()))
if(elapsed is not None):
print 'Elapsed time: {}n'.format(elapsed)
def endlog(self):
"""Log time for the end of execution with elapsed time.
"""
self.log('=> End Timing: {}', self.now())
def now(self):
"""Return current elapsed time as hh:mm:ss string.
:return: String.
"""
return str(dt.timedelta(seconds = self.clock() - self.start))
def _secondsToStr(self, sec):
"""Convert timestamp to h:mm:ss string.
:param sec: Timestamp.
"""
return str(dt.datetime.fromtimestamp(sec))
answered Jan 29, 2015 at 15:42
GallGall
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In IPython, «timeit» any script:
def foo():
%run bar.py
timeit foo()
answered May 20, 2015 at 14:40
B.KocisB.Kocis
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Use line_profiler.
line_profiler will profile the time individual lines of code take to execute. The profiler is implemented in C via Cython in order to reduce the overhead of profiling.
from line_profiler import LineProfiler
import random
def do_stuff(numbers):
s = sum(numbers)
l = [numbers[i]/43 for i in range(len(numbers))]
m = ['hello'+str(numbers[i]) for i in range(len(numbers))]
numbers = [random.randint(1,100) for i in range(1000)]
lp = LineProfiler()
lp_wrapper = lp(do_stuff)
lp_wrapper(numbers)
lp.print_stats()
The results will be:
Timer unit: 1e-06 s
Total time: 0.000649 s
File: <ipython-input-2-2e060b054fea>
Function: do_stuff at line 4
Line # Hits Time Per Hit % Time Line Contents
==============================================================
4 def do_stuff(numbers):
5 1 10 10.0 1.5 s = sum(numbers)
6 1 186 186.0 28.7 l = [numbers[i]/43 for i in range(len(numbers))]
7 1 453 453.0 69.8 m = ['hello'+str(numbers[i]) for i in range(len(numbers))]
answered Mar 28, 2018 at 5:43
Yu JiaaoYu Jiaao
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1
I used a very simple function to time a part of code execution:
import time
def timing():
start_time = time.time()
return lambda x: print("[{:.2f}s] {}".format(time.time() - start_time, x))
And to use it, just call it before the code to measure to retrieve function timing, and then call the function after the code with comments. The time will appear in front of the comments. For example:
t = timing()
train = pd.read_csv('train.csv',
dtype={
'id': str,
'vendor_id': str,
'pickup_datetime': str,
'dropoff_datetime': str,
'passenger_count': int,
'pickup_longitude': np.float64,
'pickup_latitude': np.float64,
'dropoff_longitude': np.float64,
'dropoff_latitude': np.float64,
'store_and_fwd_flag': str,
'trip_duration': int,
},
parse_dates = ['pickup_datetime', 'dropoff_datetime'],
)
t("Loaded {} rows data from 'train'".format(len(train)))
Then the output will look like this:
[9.35s] Loaded 1458644 rows data from 'train'
answered Aug 7, 2018 at 5:42
Tao WangTao Wang
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I tried and found time difference using the following scripts.
import time
start_time = time.perf_counter()
[main code here]
print (time.perf_counter() - start_time, "seconds")
answered May 8, 2020 at 4:44
Hafez AhmadHafez Ahmad
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1
You do this simply in Python. There is no need to make it complicated.
import time
start = time.localtime()
end = time.localtime()
"""Total execution time in minutes$ """
print(end.tm_min - start.tm_min)
"""Total execution time in seconds$ """
print(end.tm_sec - start.tm_sec)
swateek
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answered Feb 16, 2019 at 5:18
1
Later answer, but I use the built-in timeit
:
import timeit
code_to_test = """
a = range(100000)
b = []
for i in a:
b.append(i*2)
"""
elapsed_time = timeit.timeit(code_to_test, number=500)
print(elapsed_time)
# 10.159821493085474
- Wrap all your code, including any imports you may have, inside
code_to_test
. number
argument specifies the amount of times the code should repeat.- Demo
answered Feb 25, 2020 at 0:15
Pedro LobitoPedro Lobito
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Timeit is a class in Python used to calculate the execution time of small blocks of code.
Default_timer is a method in this class which is used to measure the wall clock timing, not CPU execution time. Thus other process execution might interfere with this. Thus it is useful for small blocks of code.
A sample of the code is as follows:
from timeit import default_timer as timer
start= timer()
# Some logic
end = timer()
print("Time taken:", end-start)
answered Nov 16, 2017 at 2:16
0
First, install humanfriendly package by opening Command Prompt (CMD) as administrator and type there —
pip install humanfriendly
Code:
from humanfriendly import format_timespan
import time
begin_time = time.time()
# Put your code here
end_time = time.time() - begin_time
print("Total execution time: ", format_timespan(end_time))
Output:
Georgy
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answered Apr 16, 2020 at 10:40
Amar KumarAmar Kumar
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Following this answer created a simple but convenient instrument.
import time
from datetime import timedelta
def start_time_measure(message=None):
if message:
print(message)
return time.monotonic()
def end_time_measure(start_time, print_prefix=None):
end_time = time.monotonic()
if print_prefix:
print(print_prefix + str(timedelta(seconds=end_time - start_time)))
return end_time
Usage:
total_start_time = start_time_measure()
start_time = start_time_measure('Doing something...')
# Do something
end_time_measure(start_time, 'Done in: ')
start_time = start_time_measure('Doing something else...')
# Do something else
end_time_measure(start_time, 'Done in: ')
end_time_measure(total_start_time, 'Total time: ')
The output:
Doing something...
Done in: 0:00:01.218000
Doing something else...
Done in: 0:00:01.313000
Total time: 0:00:02.672000
answered Nov 26, 2020 at 13:05
Nick LegendNick Legend
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This is Paul McGuire’s answer that works for me. Just in case someone was having trouble running that one.
import atexit
from time import clock
def reduce(function, iterable, initializer=None):
it = iter(iterable)
if initializer is None:
value = next(it)
else:
value = initializer
for element in it:
value = function(value, element)
return value
def secondsToStr(t):
return "%d:%02d:%02d.%03d" %
reduce(lambda ll,b : divmod(ll[0],b) + ll[1:],
[(t*1000,),1000,60,60])
line = "="*40
def log(s, elapsed=None):
print (line)
print (secondsToStr(clock()), '-', s)
if elapsed:
print ("Elapsed time:", elapsed)
print (line)
def endlog():
end = clock()
elapsed = end-start
log("End Program", secondsToStr(elapsed))
def now():
return secondsToStr(clock())
def main():
start = clock()
atexit.register(endlog)
log("Start Program")
Call timing.main()
from your program after importing the file.
answered Apr 8, 2015 at 0:24
Saurabh RanaSaurabh Rana
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The time of a Python program’s execution measure could be inconsistent depending on:
- Same program can be evaluated using different algorithms
- Running time varies between algorithms
- Running time varies between implementations
- Running time varies between computers
- Running time is not predictable based on small inputs
This is because the most effective way is using the «Order of Growth» and learn the Big «O» notation to do it properly.
Anyway, you can try to evaluate the performance of any Python program in specific machine counting steps per second using this simple algorithm:
adapt this to the program you want to evaluate
import time
now = time.time()
future = now + 10
step = 4 # Why 4 steps? Because until here already four operations executed
while time.time() < future:
step += 3 # Why 3 again? Because a while loop executes one comparison and one plus equal statement
step += 4 # Why 3 more? Because one comparison starting while when time is over plus the final assignment of step + 1 and print statement
print(str(int(step / 10)) + " steps per second")
answered Jul 31, 2017 at 15:13
ManuManu
1124 bronze badges
After reading this article, you’ll learn: –
- How to calculate the program’s execution time in Python
- Measure the total time elapsed to execute the code block in seconds, milliseconds, minutes, and hours
- Also, get the execution time of functions and loops.
In this article, We will use the following four ways to measure the execution time in Python: –
time.time()
function: measure the the total time elapsed to execute the script in seconds.time.process_time()
: measure the CPU execution time of a code- timeit module: measure the execution time of a small piece of a code including the single line of code as well as multiple lines of code
- DateTime module: measure the execution time in the hours-minutes-seconds format.
To measure the code performance, we need to calculate the time taken by the script/program to execute. Measuring the execution time of a program or parts of it will depend on your operating system, Python version, and what you mean by ‘time’.
Before proceeding further, first, understand what time is.
Table of contents
- Wall time vs. CPU time
- How to Measure Execution Time in Python
- Example: Get Program’s Execution Time in Seconds
- Get Execution Time in Milliseconds
- Get Execution Time in Minutes
- Get Program’s CPU Execution Time using process_time()
- timeit module to measure the execution time of a code
- Example: Measure the execution time of a function
- Measure the execution time of a single line of code
- Measure the execution time of a multiple lines of code
- DateTime Module to determine the script’s execution time
- Conclusion
Wall time vs. CPU time
We often come across two terms to measure the execution time: Wall clock time and CPU time.
So it is essential to define and differentiate these two terms.
- Wall time (also known as clock time or wall-clock time) is simply the total time elapsed during the measurement. It’s the time you can measure with a stopwatch. It is the difference between the time at which a program finished its execution and the time at which the program started. It also includes waiting time for resources.
- CPU Time, on the other hand, refers to the time the CPU was busy processing the program’s instructions. The time spent waiting for other task to complete (like I/O operations) is not included in the CPU time. It does not include the waiting time for resources.
The difference between the Wall time and CPU time can occur from architecture and run-time dependency, e.g., programmed delays or waiting for system resources to become available.
For example, a program reports that it has used “CPU time 0m0.2s, Wall time 2m4s”. It means the program was active for 2 minutes and four seconds. Still, the computer’s processor spent only 0.2 seconds performing calculations for the program. May be program was waiting for some resources to become available.
At the beginning of each solution, I listed explicitly which kind of time each method measures.
So depending upon why you are measuring your program’s execution time, you can choose to calculate the Wall or CPU time.
The Python time module provides various time-related functions, such as getting the current time and suspending the calling thread’s execution for the given number of seconds. The below steps show how to use the time module to calculate the program’s execution time.
- Import time module
The time module comes with Python’s standard library. First, Import it using the import statement.
- Store the start time
Now, we need to get the start time before executing the first line of the program. To do this, we will use the
time()
function to get the current time and store it in a ‘start_time‘ variable before the first line of the program.
Thetime()
function of a time module is used to get the time in seconds since epoch. The handling of leap seconds is platform-dependent. - Store the end time
Next, we need to get the end time before executing the last line.
Again, we will use thetime()
function to get the current time and store it in the ‘end_time‘ variable before the last line of the program. - Calculate the execution time
The difference between the end time and start time is the execution time. Get the execution time by subtracting the start time from the end time.
Example: Get Program’s Execution Time in Seconds
Use this solution in the following cases: –
- Determine the execution time of a script
- Measure the time taken between lines of code.
Note: This solution measures the Wall time, i.e., total elapsed time, not a CPU time.
import time
# get the start time
st = time.time()
# main program
# find sum to first 1 million numbers
sum_x = 0
for i in range(1000000):
sum_x += i
# wait for 3 seconds
time.sleep(3)
print('Sum of first 1 million numbers is:', sum_x)
# get the end time
et = time.time()
# get the execution time
elapsed_time = et - st
print('Execution time:', elapsed_time, 'seconds')
Output:
Sum of first 1 million numbers is: 499999500000 Execution time: 3.125561475753784 seconds
Note: It will report more time if your computer is busy with other tasks. If your script was waiting for some resources, the execution time would increase because the waiting time will get added to the final result.
Get Execution Time in Milliseconds
Use the above example to get the execution time in seconds, then multiply it by 1000 to get the final result in milliseconds.
Example:
# get execution time in milliseconds
res = et - st
final_res = res * 1000
print('Execution time:', final_res, 'milliseconds')
Output:
Sum of first 1 million numbers is: 499999500000
Execution time: 3125.988006591797 milliseconds
Get Execution Time in Minutes
Use the above example to get the execution time in seconds, then divide it by 60 to get the final result in minutes.
Example:
# get execution time in minutes
res = et - st
final_res = res / 60
print('Execution time:', final_res, 'minutes')
Output:
Sum of first 1 million numbers is: 499999500000 Execution time: 0.05200800895690918 minutes
Do you want better formatting?
Use the strftime() to convert the time in a more readable format like (hh-mm-ss) hours-minutes-seconds.
import time
st = time.time()
# your code
sum_x = 0
for i in range(1000000):
sum_x += i
time.sleep(3)
print('Sum:', sum_x)
elapsed_time = time.time() - st
print('Execution time:', time.strftime("%H:%M:%S", time.gmtime(elapsed_time)))
Output:
Sum: 499999500000
Execution time: 00:00:03
Get Program’s CPU Execution Time using process_time()
The time.time()
will measure the wall clock time. If you want to measure the CPU execution time of a program use the time.process_time()
instead of time.time()
.
Use this solution if you don’t want to include the waiting time for resources in the final result. Let’s see how to get the program’s CPU execution time.
import time
# get the start time
st = time.process_time()
# main program
# find sum to first 1 million numbers
sum_x = 0
for i in range(1000000):
sum_x += i
# wait for 3 seconds
time.sleep(3)
print('Sum of first 1 million numbers is:', sum_x)
# get the end time
et = time.process_time()
# get execution time
res = et - st
print('CPU Execution time:', res, 'seconds')
Output:
Sum of first 1 million numbers is: 499999500000 CPU Execution time: 0.234375 seconds
Note:
Because we are calculating the CPU execution time of a program, as you can see, the program was active for more than 3 seconds. Still, those 3 seconds were not added in CPU time because the CPU was ideal, and the computer’s processor spent only 0.23 seconds performing calculations for the program.
timeit module to measure the execution time of a code
Python timeit module provides a simple way to time small piece of Python code. It has both a Command-Line Interface as well as a callable one. It avoids many common traps for measuring execution times.
timeit module is useful in the following cases: –
- Determine the execution time of a small piece of code such as functions and loops
- Measure the time taken between lines of code.
The timeit()
function: –
The timeit.timeit()
returns the time (in seconds) it took to execute the code number times.
timeit.timeit(stmt='pass', setup='pass', timer=<default timer>, number=1000000, globals=None)
Note: This solution measures the Wall time, i.e., total elapsed time, not a CPU time.
The below steps show how to measure the execution time of a code using the timeit module.
- First, create a Timer instance using the
timeit()
function - Next, Pass a code at the place of the
stmt
argument. stmt is the code for which we want to measure the time - Next, If you wish to execute a few statements before your actual code, pass them to the setup argument like import statements.
- To set a timer value, we will use the default timer provided by Python.
- Next, decide how many times you want to execute the code and pass it to the number argument. The default value of number is 1,000,000.
- In the end, we will execute the
timeit()
function with the above values to measure the execution time of the code
Example: Measure the execution time of a function
Here we will calculate the execution time of an ‘addition()’ function. We will run the addition()
function five-time to get the average execution time.
import timeit
# print addition of first 1 million numbers
def addition():
print('Addition:', sum(range(1000000)))
# run same code 5 times to get measurable data
n = 5
# calculate total execution time
result = timeit.timeit(stmt='addition()', globals=globals(), number=n)
# calculate the execution time
# get the average execution time
print(f"Execution time is {result / n} seconds")
Output:
Addition: 499999500000 Addition: 499999500000 Addition: 499999500000 Addition: 499999500000 Addition: 499999500000 Execution time is 0.03770382 seconds
Note:
If you run time-consuming code with the default number
value, it will take a lot of time. So assign less value to the number
argument Or decide how many samples do you want to measure to get the accurate execution time of a code.
- The
timeit()
functions disable the garbage collector, which results in accurate time capture. - Also, using the
timeit()
function, we can repeat the execution of the same code as many times as we want, which minimizes the influence of other tasks running on your operating system. Due to this, we can get the more accurate average execution time.
Measure the execution time of a single line of code
Run the %timeit
command on a command-line or jupyter notebook to get the execution time of a single line of code.
Example: Use %timeit
just before the line of code
%timeit [x for x in range(1000)]
# Output
2.08 µs ± 223 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
Also, we can customize the command using the various options to enhance the profiling and capture a more accurate execution time.
- Define the number of runs using the
-r
option. For example,%timeit -r10 your_code
means run the code line 10 times. - Define the loops within each run using the
-r
and-n
option. - If you ommit the options be default it is 7 runs with each run having 1 million loops
Example: Customize the time profile operation to 10 runs and 20 loops within each run.
# Customizing number of runs and loops in %timeit
%timeit -r10 -n20 [x for x in range(1000)]
# output
1.4 µs ± 12.34 ns per loop (mean ± std. dev. of 10 runs, 20 loops each)
Measure the execution time of a multiple lines of code
Using the %%timeit
command, we can measure the execution time of multiple lines of code. The command options will remain the same.
Note: you need to replace the single percentage (%
) with double percentage (%%
) in the timeit command to get the execution time of multiple lines of a code
Example:
# Time profiling using %%timeit
%%timeit -r5 -n10
# find sum to first 1 million numbers
sum_x = 0
for i in range(1000000):
sum_x += i
# Output
10.5 µs ± 226 ns per loop (mean ± std. dev. of 5 runs, 10 loops each)
DateTime Module to determine the script’s execution time
Also, you can use the Datetime module to measure the program’s running time. Use the below steps.
Import DateTime module
- Next, store the start time using the
datetime.now()
function before the first line of a script - Next, save the end time before using the same function before the last line of a script
- In the end, calculate the execution time by subtracting the start time from an end time
Note: This solution measures the Wall time, i.e., total elapsed time, not a CPU time.
Example:
import datetime
import time
# get the start datetime
st = datetime.datetime.now()
# main program
# find sum to first 1 million numbers
sum_x = 0
for i in range(1000000):
sum_x += i
# wait for 3 seconds
time.sleep(3)
print('Sum of first 1 million numbers is:', sum_x)
# get the end datetime
et = datetime.datetime.now()
# get execution time
elapsed_time = et - st
print('Execution time:', elapsed_time, 'seconds')
Output:
Sum of first 1 million numbers is: 499999500000 Execution time: 0:00:03.115498 seconds
Conclusion
Python provides several functions to get the execution time of a code. Also, we learned the difference between Wall-clock time and CPU time to understand which execution time we need to measure.
Use the below functions to measure the program’s execution time in Python:
time.time()
: Measure the the total time elapsed to execute the code in seconds.timeit.timeit()
: Simple way to time a small piece of Python code%timeit
and%%timeit
: command to get the execution time of a single line of code and multiple lines of code.datetime.datetime.now()
: Get execution time in hours-minutes-seconds format
Also, use the time.process_time()
function to get the program’s CPU execution time.
Чтобы измерить время выполнения программы, используйте функции time.clock() или time.time(). Документы Python утверждают, что эта функция должна использоваться для целей тестирования.
Пример
import time t0= time.clock() print("Hello") t1 = time.clock() - t0 print("Time elapsed: ", t1 - t0) # CPU seconds elapsed (floating point)
Вывод
Это даст вывод —
Time elapsed: 0.0009403145040156798
Вы также можете использовать модуль timeit для правильного статистического анализа времени выполнения фрагмента кода. Он запускает фрагмент несколько раз, а затем сообщает, сколько времени занял самый короткий цикл. Вы можете использовать его следующим образом —
Пример
def f(x): return x * x import timeit timeit.repeat("for x in range(100): f(x)", "from __main__ import f", number=100000)
Вывод
Это даст вывод —
[2.0640320777893066, 2.0876040458679199, 2.0520210266113281]
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Допустим, вам необходимо узнать, сколько времени занимает выполнение той или иной функции. Используя модуль time, вы можете рассчитать это время.
import time startTime = time.time() # время начала замера # здесь пишем код, время которого необходимо измерить endTime = time.time() #время конца замера totalTime = endTime - startTime #вычисляем затраченное время print("Время, затраченное на выполнение данного кода = ", totalTime)
Допустим, вы хотите знать время выполнения следующего кода Python:
a = range(100000)
b = []
for i in a:
b.append(i*2)
Есть несколько способов измерить время, необходимое для выполнения скрипта Python, но вот лучший способ сделать это, и я объясню почему:
import timeit
code_to_test = """
a = range(100000)
b = []
for i in a:
b.append(i*2)
"""
elapsed_time = timeit.timeit(code_to_test, number=100)/100
print(elapsed_time)
В консоли получим: 0.01137321546
Это вывод, который я получаю на своем Macbook Pro. Итак, это более или менее 1/100 секунды.
Как работает вышеуказанный скрипт
Строка 1: мы импортируем модуль timeit
. Строка 3: мы создаем переменную. В этой переменной мы храним код, который хотим протестировать. Этот код должен идти внутри тройных кавычек. Итак, тестовый код предоставляется в виде строки. Строка 10: мы вызываем функцию time.timeit()
. Функция timeit()
получает тестовый код в качестве аргумента, выполняет его и записывает время выполнения. Чтобы получить точное время, я приказал timeit()
выполнить 100 циклов. Поэтому мне пришлось разделить вывод на 100, чтобы получить время выполнения только для одного цикла. Строка 11: мы просто распечатываем время выполнения. Результат — время выполнения в секундах.
Почему timeit() — лучший способ измерить время выполнения кода Python?
1. timeit()
автоматически будет использовать time.clock()
или time.time()
для вас в фоновом режиме, в зависимости от того, какая операционная система вам нужна для получения наиболее точных результатов.
2. timeit()
отключает сборщик мусора, который может исказить результаты.
3. timeit()
повторяет тест много раз (в нашем случае 100 раз), чтобы минимизировать влияние других задач, выполняемых в вашей операционной системе.
Упражнение:
Кстати, код, который мы тестировали выше, строит список путем умножения элементов другого списка. Я могу достичь того же результата, используя range
:
a = range(100000)
b = [i*2 for i in a]
Если вам больше нечем заняться и попробуйте выполнить упражнение, попробуйте измерить время выполнения приведенного выше кода с помощью timeit()
.
Наконец, совет: закрывайте тяжелые программы, которые запускаются на вашем компьютере, когда вы выполняете такие тесты, чтобы вы получили еще более точные результаты, которые не зависят от тяжелых задач процессора.