timeit: Additional changes for autorange

[csabella]

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

[csabella]

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.

[csabella]

Assigning to @Mariatta for the sprints.

[alessandrocucci]

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

[csabella]

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

[stevendaprano]

@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.

[stevendaprano]

(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.)

[stevendaprano]

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?

[stevendaprano]

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:

1. 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

2. 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.)