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date, time and datetime alternate constructors should take fast construction path #76584

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pganssle opened this issue Dec 21, 2017 · 4 comments
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3.7 3.8 type-feature

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@pganssle
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@pganssle pganssle commented Dec 21, 2017

BPO 32403
Nosy @abalkin, @pganssle
PRs
  • #4993
  • #5814
  • #5929
  • 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 = <Date 2018-01-16.18:07:46.382>
    created_at = <Date 2017-12-21.21:51:14.443>
    labels = ['3.8', 'type-feature', '3.7']
    title = 'date, time and datetime alternate constructors should take fast construction path'
    updated_at = <Date 2018-02-27.19:58:30.646>
    user = 'https://github.com/pganssle'

    bugs.python.org fields:

    activity = <Date 2018-02-27.19:58:30.646>
    actor = 'belopolsky'
    assignee = 'none'
    closed = True
    closed_date = <Date 2018-01-16.18:07:46.382>
    closer = 'belopolsky'
    components = []
    creation = <Date 2017-12-21.21:51:14.443>
    creator = 'p-ganssle'
    dependencies = []
    files = []
    hgrepos = []
    issue_num = 32403
    keywords = ['patch']
    message_count = 4.0
    messages = ['308907', '310099', '313019', '313021']
    nosy_count = 2.0
    nosy_names = ['belopolsky', 'p-ganssle']
    pr_nums = ['4993', '5814', '5929']
    priority = 'normal'
    resolution = None
    stage = 'resolved'
    status = 'closed'
    superseder = None
    type = 'enhancement'
    url = 'https://bugs.python.org/issue32403'
    versions = ['Python 3.7', 'Python 3.8']

    @pganssle
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    @pganssle pganssle commented Dec 21, 2017

    In the addition of the fromisoformat() alternate constructor (bpo-15873: #4699), I noted that I was able to get some significant speedup by special-casing the datetime baseclass in the C code so that it bypasses the Python constructor, by replacing code that looks like this:

    return PyObject_CallFunction(cls, "iii", year, month, day);
    

    With code that looks like this:

        PyObject *result;
        if ( (PyTypeObject *)cls == & PyDateTime_DateType ) {
            result = new_date_ex(year, month, day, (PyTypeObject *)cls);
        } else {
            result = PyObject_CallFunction(cls, "iii", year, month, day);
        }
    return result;
    

    (This is for date, but the results are even more striking for datetime).

    In my initial proof of concept implementation of a new_date_subclass_ex method, I've seen (this is not compiled with optimizations on, mind you) speedups for the other constructors as well:

    Old constructor:
    \================
    Class: date
    constructor:        940.5ns
    date.fromordinal:   1544.8ns
    date.fromtimestamp: 1941.9ns
    
    Class: DateSubclass
    constructor:        1016.6ns
    date.fromordinal:   1760.3ns
    date.fromtimestamp: 2295.3ns
    
    
    With fastpath:
    \==============
    Class: date
    constructor:        964.3ns
    date.fromordinal:   997.6ns
    date.fromtimestamp: 1130.2ns
    
    Class: DateSubclass
    constructor:        1086.9ns
    date.fromordinal:   1818.5ns
    date.fromtimestamp: 2129.9ns
    

    As you can see, this is a fairly significant speedup in the common case with no cost in the unusual case and no change in behavior. I propose that we switch over all the C constructors where it makes sense to do so in date, time and datetime.

    I'll have a PR forthcoming soon.

    @pganssle pganssle added 3.7 3.8 type-feature labels Dec 21, 2017
    @abalkin
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    @abalkin abalkin commented Jan 16, 2018

    New changeset 9f1b7b9 by Alexander Belopolsky (Paul Ganssle) in branch 'master':
    bpo-32403: Faster date and datetime constructors (bpo-4993)
    9f1b7b9

    @abalkin abalkin closed this as completed Jan 16, 2018
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    @abalkin abalkin commented Feb 27, 2018

    New changeset 5bd04f9 by Alexander Belopolsky (Paul Ganssle) in branch 'master':
    bpo-10381, bpo-32403: What's new entries for changes to datetime (gh-5814)
    5bd04f9

    @abalkin
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    @abalkin abalkin commented Feb 27, 2018

    New changeset fff596f by Alexander Belopolsky (Miss Islington (bot)) in branch '3.7':
    bpo-10381, bpo-32403: What's new entries for changes to datetime (gh-5814) (gh-5929)
    fff596f

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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