154 lines
5.6 KiB
Plaintext
154 lines
5.6 KiB
Plaintext
Metadata-Version: 2.1
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Name: isoduration
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Version: 20.11.0
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Summary: Operations with ISO 8601 durations
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Home-page: https://github.com/bolsote/isoduration
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Author: Víctor Muñoz
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Author-email: victorm@marshland.es
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License: UNKNOWN
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Project-URL: Repository, https://github.com/bolsote/isoduration
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Project-URL: Bug Reports, https://github.com/bolsote/isoduration/issues
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Project-URL: Changelog, https://github.com/bolsote/isoduration/blob/master/CHANGELOG
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Keywords: datetime,date,time,duration,duration-parsing,duration-string,iso8601,iso8601-duration
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Platform: UNKNOWN
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Classifier: Programming Language :: Python :: 3
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Classifier: Operating System :: OS Independent
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Classifier: License :: OSI Approved :: ISC License (ISCL)
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Classifier: Development Status :: 4 - Beta
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Classifier: Intended Audience :: Developers
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Classifier: Topic :: Software Development :: Libraries :: Python Modules
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Requires-Python: >=3.7
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Description-Content-Type: text/markdown
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Requires-Dist: arrow (>=0.15.0)
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# isoduration: Operations with ISO 8601 durations.
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[![PyPI Package](https://img.shields.io/pypi/v/isoduration?style=flat-square)](https://pypi.org/project/isoduration/)
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## What is this.
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ISO 8601 is most commonly known as a way to exchange datetimes in textual format. A
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lesser known aspect of the standard is the representation of durations. They have a
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shape similar to this:
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```
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P3Y6M4DT12H30M5S
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```
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This string represents a duration of 3 years, 6 months, 4 days, 12 hours, 30 minutes,
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and 5 seconds.
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The state of the art of ISO 8601 duration handling in Python is more or less limited to
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what's offered by [`isodate`](https://pypi.org/project/isodate/). What we are trying to
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achieve here is to address the shortcomings of `isodate` (as described in their own
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[_Limitations_](https://github.com/gweis/isodate/#limitations) section), and a few of
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our own annoyances with their interface, such as the lack of uniformity in their
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handling of types, and the use of regular expressions for parsing.
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## How to use it.
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This package revolves around the [`Duration`](src/isoduration/types.py) type.
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Given a ISO duration string we can produce such a type by using the `parse_duration()`
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function:
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```py
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>>> from isoduration import parse_duration
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>>> duration = parse_duration("P3Y6M4DT12H30M5S")
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>>> duration.date
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DateDuration(years=Decimal('3'), months=Decimal('6'), days=Decimal('4'), weeks=Decimal('0'))
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>>> duration.time
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TimeDuration(hours=Decimal('12'), minutes=Decimal('30'), seconds=Decimal('5'))
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```
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The `date` and `time` portions of the parsed duration are just regular
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[dataclasses](https://docs.python.org/3/library/dataclasses.html), so their members can
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be accessed in a non-surprising way.
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Besides just parsing them, a number of additional operations are available:
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- Durations can be compared and negated:
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```py
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>>> parse_duration("P3Y4D") == parse_duration("P3Y4DT0H")
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True
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>>> -parse_duration("P3Y4D")
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Duration(DateDuration(years=Decimal('-3'), months=Decimal('0'), days=Decimal('-4'), weeks=Decimal('0')), TimeDuration(hours=Decimal('0'), minutes=Decimal('0'), seconds=Decimal('0')))
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```
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- Durations can be added to, or subtracted from, Python datetimes:
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```py
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>>> from datetime import datetime
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>>> datetime(2020, 3, 15) + parse_duration("P2Y")
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datetime.datetime(2022, 3, 15, 0, 0)
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>>> datetime(2020, 3, 15) - parse_duration("P33Y1M4D")
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datetime.datetime(1987, 2, 11, 0, 0)
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```
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- Durations are hashable, so they can be used as dictionary keys or as part of sets.
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- Durations can be formatted back to a ISO 8601-compliant duration string:
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```py
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>>> from isoduration import parse_duration, format_duration
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>>> format_duration(parse_duration("P11YT2H"))
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'P11YT2H'
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>>> str(parse_duration("P11YT2H"))
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'P11YT2H'
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```
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## How to improve it.
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These steps, in this order, should land you in a development environment:
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```sh
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git clone git@github.com:bolsote/isoduration.git
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cd isoduration/
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python -m venv ve
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. ve/bin/activate
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pip install -U pip
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pip install -e .
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pip install -r requirements/dev.txt
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```
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Adapt to your own likings and/or needs.
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Testing is driven by [tox](https://tox.readthedocs.io). The output of `tox -l` and a
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careful read of [tox.ini](tox.ini) should get you there.
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## FAQs.
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### How come `P1Y != P365D`?
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Some years have 366 days. If it's not always the same, then it's not the same.
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### Why do you create your own types, instead of somewhat shoehorning a `timedelta`?
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`timedelta` cannot represent certain durations, such as those involving years or months.
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Since it cannot represent all possible durations without dangerous arithmetic, then it
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must not be the right type.
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### Why don't you use regular expressions to parse duration strings?
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[Regular expressions should only be used to parse regular languages.](https://stackoverflow.com/a/1732454)
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### Why is parsing the inverse of formatting, but the converse is not true?
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Because this wonderful representation is not unique.
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### Why do you support `<insert here a weird case>`?
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Probably because the standard made me to.
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### Why do you not support `<insert here a weird case>`?
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Probably because the standard doesn't allow me to.
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### Why is it not possible to subtract a datetime from a duration?
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I'm confused.
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### Why should I use this over some other thing?
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You shouldn't do what people on the Internet tell you to do.
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### Why are ISO standards so strange?
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Yes.
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## References.
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- [XML Schema Part 2: Datatypes, Appendix D](https://www.w3.org/TR/xmlschema-2/#isoformats):
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This excitingly named document contains more details about ISO 8601 than any human
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should be allowed to understand.
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- [`isodate`](https://pypi.org/project/isodate/): The original implementation of ISO
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durations in Python. Worth a look. But ours is cooler.
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