timeit: Additional changes for autorange

@stevendaprano

BPO	36461
Nosy	@stevendaprano, @alessandrocucci, @csabella, @mangrisano
PRs	bpo-36461: Added the total_time parameter to the timeit.autorange() function. #12953 gh-80642: timeit - Additional changes for autorange #12954

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-03-28.09:49:28.109>
labels = ['3.7', '3.8', 'type-feature', 'library', 'easy']
title = 'timeit: Additional changes for autorange'
updated_at = <Date 2019-06-01.10:54:11.435>
user = 'https://github.com/csabella'

bugs.python.org fields:

activity = <Date 2019-06-01.10:54:11.435>
actor = 'steven.daprano'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-03-28.09:49:28.109>
creator = 'cheryl.sabella'
dependencies = []
files = []
hgrepos = []
issue_num = 36461
keywords = ['patch', 'easy']
message_count = 12.0
messages = ['339025', '339027', '340541', '343388', '343394', '343400', '343403', '343409', '343454', '343484', '344166', '344167']
nosy_count = 4.0
nosy_names = ['steven.daprano', 'acucci', 'cheryl.sabella', 'mangrisano']
pr_nums = ['12953', '12954']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue36461'
versions = ['Python 3.7', 'Python 3.8']

Linked PRs

gh-80642: timeit - make target time of autorange configurable #140283

bpo-6422 implemented the autorange function for timeit, but in msg272704, Steven D'Aprano outlined follow-up change requests to that patch.

make the 0.2s time configurable;
have timeit and repeat methods (and functions) fall back
on autorange if the number is set to 0 or None.

Opening this ticket for those change requests.

@Mariatta

Assigning to @Mariatta for the sprints.

@Mariatta

Hello @Mariatta,
if this is simple I would like to work on that, can I?
Thanks!

@steven.daprano, would you be able to review the pull requests based on your original concept for this change? Thank you!

@steven.daprano, would you be able to review the pull requests based
on your original concept for this change? Thank you!

With difficulty... for technology/financial reasons, I don't have a
browser that works properly with github. But I'll do what I can.

(Sorry, I can't comment on Github.)

Looking at PR 12954:

I'm not sure about the API for making the time used by autorange configurable. The time taken is only used when autoranging, but the API takes it as an argument to the constructor even if it won't be used. I haven't thought deeply about this for a few years, so now I'm wondering if this is the best API. Let me think some more.

However, the parameter name "max_time_taken" is certainly wrong: it can be wrongly read as meaning the maximum time the sample code will run, which is not the case.

Also, it is not a maximum time, it is a minimum time: the autoranger increases the number of loops until it takes at least max_time_taken seconds, not at most.

So I think a better name might be something like target_time. It suggests a time we are targeting, not one we promise to hit precisely, it doesn't mislead into thinking it will be the total time. And it is a bit shorter without being cryptically short.

Anyone have any better suggestions for the parameter name?

Likewise I suggest default_target_time for the global (line 62).

With the longer parameter list, there's a couple of places that the line length seems to exceed 79 columns, e.g. lines 244, 272.

Line 176: I think that should be ``if number == 0:`` since we don't want to accept any arbitrary falsey value, just zero.

NEWS line 4: take out the reference to None.

(I haven't reviewed the tests at this stage.)

Looking at PR 12953:

The only API for setting the target time is by passing it to the autorange method directly. So I think that there's no way for the caller of Timer.timeit() or Timer.repeat() to specify a custom target time, is that right?

Michele, Alessandro, thank you both for your work! And thank you Cheryl for managing this ticket.

I like mangrisano's design where the target time is passed as an argument to the autorange method, although I prefer the name "target_time". (But I'm open to alternatives.)

So I think a good approach might be a hybrid between mangrisano's design, and the design by Alessandro:

the constructor takes the target time and records it as an attribute;

def __init__(self, ..., target_time=default_target_time):
    self.target_time = target_time

when the timeit method is used, if number=0 the target time is taken from self.target_time and passed to autorange;

if the autorange method is called directly, the caller can override the target time by passing it as argument; otherwise the default value is looked up from the instance attribute.

So something like

def autorange(self, callback=None, target_time=None):
    if target_time is None:
        target_time = self.target_time
    ...

Please suggest alternatives or point out anything I may have missed, and thank you all again!

(I'm now going to be away from the keyboard for at least the next 18 hours so if I don't reply quickly, that's why.)

Sorry for the late reply.

Just a question: why we need to check ``if number == 0:``? In the
proposal you asked for None too. What changed? Even if the function is
called with False, will it hurts to keep the default value?

Fair question. On rethinking, I'm okay with an explicit check for None
or zero, if number is None or number < 0 but I don't like the idea
of accepting any falsey value.

Calling the function with False is fine, since False == 0 but I don't
think it is fine to call the function with (say) [] or {} or "", which
are all falsey values.

if number is None or number < 0

Sorry, that should be number == 0

It looks like both the PRs have been inactive for four years, so is this still relevant? If so, can I open a new PR?

@CohenAriel

Hi @CohenAriel

Did you end up opening a new PR? I'd love to see this 0.2 be configurable.

Cheers

For whatever it's worth, I opened a new PR based on the old one and tried to get it up to date: #140283

gh-80642: timeit - make target time of autorange configurable (#140283)

pythongh-80642: timeit - make target time of autorange configurable (p…

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timeit: Additional changes for autorange #80642

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csabella commented on Mar 28, 2019

csabella commented on Mar 28, 2019

alessandrocucci commented on Apr 19, 2019

csabella commented on May 24, 2019

stevendaprano commented on May 24, 2019

stevendaprano commented on May 24, 2019

stevendaprano commented on May 24, 2019

stevendaprano commented on May 24, 2019

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stevendaprano commented on Jun 1, 2019

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