如何让 Python timeit 模块不重复循环中的最后一次迭代

Question

I am doing some load testing using timeit. I am looping through a list. In everything I have tried, timeit repeats the last value in the list 3 times. I know that repeat defaults to 3. I've tried not using repeat. I've tried using repeat, but setting repeat to 0. What I want is either 0 repeats, or a repeat that picks up the correct parameter instead of repeating the last parameter 3 times. I'll show you what I've tried, and then the expected results, and the actual results.

My module is named z_sandbox.py, and I am calling this in the module, by executing within VS Code. I am not using the command line.

I've tried three different options:

Option #1: timeit.Timer, with no repeats specified.

import timeit
params = ["param1", "param2", "param3"]
print("*****START*****")
for param in params:  
    print('STARTING: %s ' % (param))   
    timeit.Timer(
        stmt="print('%s ' % (z_sandbox.param))",
        setup="import z_sandbox"
    ).timeit(number=3)
print("*****DONE*****")

Expected Results:

In the above I am not using a repeat, so I would expect no repeats, and exactly 3 executions of each statement, for a total of 9 executions.

Expected:

*****START*****
STARTING: param1
param1
param1
param1
STARTING: param2
param2
param2
param2
STARTING: param3
param3
param3
param3
*****DONE*****

Actual:

*****START*****
STARTING: param1
*****START*****
STARTING: param1
param1
param1
param1
STARTING: param2
param2
param2
param2
STARTING: param3
param3
param3
param3
*****DONE*****
param3
param3
param3
STARTING: param2
param3
param3
param3
STARTING: param3
param3
param3
param3
*****DONE*****

Questions: Why is "STARTING: param1" printed twice at the top? Why are the last 9 executions all param3, instead of 3 executions of each parameter? Why in the repeats is there "STARTING: param2" but then the actual execution was for param3? How do I get my expected results, which is no repeats?

Option #2: timeit.repeat, with 1 repeat specified.

timeit.repeat(
    stmt="print('%s ' % (z_sandbox.param))",
    setup="import z_sandbox",
    repeat=1,
    number=3
)

Above produces same results as Option #1.

Option #3: timeit.repeat, with 0 repeat specified.

timeit.repeat(
    stmt="print('%s ' % (z_sandbox.param))",
    setup="import z_sandbox",
    repeat=0,
    number=3
)

Above produces nothing at all.

Variation on each of above

I also tried printing the output to a file, instead of to a screen. There is no difference in the output.

How do I get my expected results, which is no repeats?

Answer 1

You can pass a callable as stmt to Timer .

timeit.Timer(stmt=lambda: print('%s ' % (param,))).timeit(number=3)

The issue with your code was that it had no main import guard to prevent the main code from occurring when the module is imported a second time. The thing about main modules is that they can be loaded twice. Once as __main__ and once under their module name.

Your code could be fixed by doing:

import timeit
params = ["param1", "param2", "param3"]
if __name__=="__main__":
    print("*****START*****")
    for idx, param in enumerate(params): 
        print('STARTING: %s ' % (param,)) 
        timeit.Timer(stmt="print('%%s ' %% (z_sandbox.params[%r]))" % (idx,), setup="import z_sandbox" ).timeit(number=3)
    print("*****DONE*****")