Hello Guiseppe,
In which circumstances:
- would this be useful?
- would a Form not be a better choice?
Best regards,
--
Aymeric.
> On 4 Feb 2019, at 00:10, Giuseppe De Marco <giuseppe.dema...@unical.it> wrote:
>
> Hi Aymeric,
>
> Thank you for the answer and for the tests as well.
> I understand and also agree your vision on all the line, I got the specific
> purpose of parse_date.
> I'd like to introduce a generalized way to parse date and datetime string
> based on Django project configuration, in settings.py.
> It could be linked, as reference, to DATE_INPUT_FORMATS or DATE_FORMATS or
> whatever better choice.
>
> This is the code example, it works as standalone, I hope that it's easy to
> read...
> ````
> # datetime_euristic_parser.py
> import re
> import datetime
>
> DATE_FORMATS = ['%Y-%m-%d',
> '%d/%m/%Y',
> '%d/%m/%y']
> DATETIME_FORMATS = ['%Y-%m-%d %H:%M:%S',
> '%d/%m/%Y %H:%M:%S',
> '%d/%m/%y %H:%M:%S',
> '%Y%m%d%H%M%SZ',
> '%Y%m%d%H%M%S.%fZ']
> # to be extended with all the matching patterns.
> DATETIME_ELEMENTS_REGEXP = {'%Y': '(?P<year>\d{4})',
> '%y': '(?P<year>\d{2})',
> '%m': '(?P<month>\d{1,2})',
> '%d': '(?P<day>\d{1,2})',
> '%H': '(?P<hour>\d{1,2})',
> '%M': '(?P<minute>\d{1,2})',
> '%S': '(?P<second>\d{1,2})',
> '%f': '(?P<microsecond>\d{6})'} # ...
>
> def datetime_regexp_builder(formats):
> """
> formats = DATE_FORMAT of DATETIME_FORMAT
> """
> regexp_dict = {}
> for df in formats:
> df_regexp = df
> for k,v in DATETIME_ELEMENTS_REGEXP.items():
> df_regexp = df_regexp.replace(k,v)
> regexp_dict[df] = df_regexp+'$'
> return regexp_dict
>
> DATE_FORMATS_REGEXP = datetime_regexp_builder(DATE_FORMATS)
> DATETIME_FORMATS_REGEXP = datetime_regexp_builder(DATETIME_FORMATS)
>
> def dformat_insp(date_str, format_regexp_dict, debug=False):
> """
> Takes a date string and returns a matching date regexp.
> """
> insp_formats = []
> for f,p in format_regexp_dict.items():
> if debug: print(date_str, f, p)
> match = re.match(p, date_str)
> if match:
> res = (f, p, {k:int(v) for k,v in match.groupdict().items()})
> insp_formats.append(res)
> return insp_formats
>
> def dateformat_insp(date_str):
> return dformat_insp(date_str, DATE_FORMATS_REGEXP)
>
> def datetimeformat_insp(date_str):
> return dformat_insp(date_str, DATETIME_FORMATS_REGEXP)
>
> def datetime_euristic_parser(value):
> """
> value can be a datestring or a datetimestring
> returns all the parsed date or datetime object
> """
> l = []
> res = dateformat_insp(value) or \
> datetimeformat_insp(value)
> for i in res:
> l.append(datetime.datetime(**i[-1]))
> return l
>
> # example
> if __name__ == '__main__':
> tests = ['04/12/2018',
> '04/12/2018 3:2:1',
> '2018-03-4 09:7:4',
> '2018-03-04T09:7:4.645194',
> '20180304121940.948000Z']
>
> for i in tests:
> res = dateformat_insp(i) or datetimeformat_insp(i)
> if res:
> print('Parsing succesfull on "{}": {}'.format(i, res))
> #print(datetime_euristic_parser(i))
> else:
> print('Parsing failed on "{}"'.format(i))
> print()
> ````
>
> I also checked these tests:
> python -m timeit -s "from django.utils.dateparse import parse_datetime"
> "parse_datetime('2019-02-03T17:27:58.645194')"
> 10000 loops, best of 3: 32.7 usec per loop
>
> python -m timeit -s "import datetime"
> "datetime.datetime.strptime('2019-02-03T17:27:58.645194',
> '%Y-%m-%dT%H:%M:%S.%f')"
> 10000 loops, best of 3: 53.5 usec per loop
>
> python -m timeit -s "from datetime_euristic_parser. import
> datetime_euristic_parser;
> datetime_euristic_parser('2019-02-03T17:27:58.645194')"
> 10000000 loops, best of 3: 0.0241 usec per loop
>
> In other words I'd like to have in Django a magic datetime parser, based on
> the settings.py global definitions, instead of iterations on try/except or
> some other custom code.
> Hope it's fun
>
> Il giorno dom 3 feb 2019 alle ore 18:44 Aymeric Augustin
> <aymeric.augus...@polytechnique.org
> <mailto:aymeric.augus...@polytechnique.org>> ha scritto:
> Hello Guiseppe,
>
> django.utils.dateparse provides helpers needed by Django to implement
> datetime, date and time fields on SQLite. (SQLite doesn't have a native date
> time type.) Their job is to parse ISO 8601 fast. That's it.
>
> A utility module should do exactly what Django needs and nothing more.
> django.utils.dateparse is documented so you can use it if it does what you
> want. If it doesn't, use something else ;-)
>
> Django forms try various formats when they receive user input because there's
> uncertainty about the format. If you're parsing user input, then you should
> use a form and you'll get the behavior you want.
>
> To clarify my point about performance, here's the function you're proposing,
> minus support for USE_L10N:
>
> def parse_datetime_alternative(value):
> for format in settings.DATETIME_INPUT_FORMATS:
> try:
> return datetime.datetime.strptime(format, value)
> except (ValueError, TypeError):
> continue
>
> It's 10 times slower than the current implementation of parse_datetime:
>
> $ python -m timeit -s "from django.conf import settings; settings.configured
> or settings.configure(); from django.utils.dateparse import
> parse_datetime_alternative as parse_datetime"
> "parse_datetime('2019-02-03T17:27:58.645194')"
> 5000 loops, best of 5: 54.2 usec per loop
>
> $ python -m timeit -s "from django.utils.dateparse import parse_datetime"
> "parse_datetime('2019-02-03T17:27:58.645194')"
> 50000 loops, best of 5: 5.48 usec per loop
>
> I implemented parse_datetime with a regex because that's almost twice as fast
> as a single call to datetime.datetime.strptime:
>
> $ python -m timeit -s "import datetime"
> "datetime.datetime.strptime('2019-02-03T17:27:58.645194',
> '%Y-%m-%dT%H:%M:%S.%f')"
> 20000 loops, best of 5: 9.87 usec per loop
>
> Best regards,
>
> --
> Aymeric.
>
>
>
>> On 3 Feb 2019, at 17:10, Giuseppe De Marco <giuseppe.dema...@unical.it
>> <mailto:giuseppe.dema...@unical.it>> wrote:
>>
>> Hi All, it's the first time for me in this ml,
>>
>> I'd like to purpose a refactor of django.utils.dateparse functions.
>> Currently a function in it, like parse_date for example, extract date time
>> string with a static regexp...
>>
>> https://docs.djangoproject.com/pl/2.1/_modules/django/utils/dateparse/
>> <https://docs.djangoproject.com/pl/2.1/_modules/django/utils/dateparse/>
>>
>> The first time I used It I thought that those functions parses date, time
>> and date time, according to settings.py definitions like
>> DATETIME_INPUT_FORMATS, but It was not this way... Then I read the code.
>>
>> Wouldn't It better to use settings.py definitions to manage these formats
>> and django.utils.dateparse behaviour?
>>
>>
>>
>>
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>
> --
> ____________________
> Dott. Giuseppe De Marco
> CENTRO ICT DI ATENEO
> University of Calabria
> 87036 Rende (CS) - Italy
> Phone: +39 0984 496945
> e-mail: giuseppe.dema...@unical.it <mailto:giuseppe.dema...@unical.it>
>
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