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python-dateutil

  • dateutil - powerful extensions to datetime — dateutil 2.8.0 documentation

    • The dateutil module provides powerful extensions to the standard datetime module, available in Python.

    Features

    • Computing of relative deltas (next month, next year, next monday, last week of month, etc);
    • Computing of relative deltas between two given date and/or datetime objects;
    • Computing of dates based on very flexible recurrence rules, using a superset of the iCalendar specification. Parsing of RFC strings is supported as well.
    • GENERIC PARSING of dates in almost any string format;
    • Timezone (tzinfo) implementations for tzfile(5) format files (/etc/localtime, /usr/share/zoneinfo, etc), TZ environment string (in all known formats), iCalendar format files, given ranges (with help from relative deltas), local machine timezone, fixed offset timezone, UTC timezone, and Windows registry-based time zones.
    • Internal UP-TO-DATE world timezone information based on Olson’s database.
    • Computing of Easter Sunday dates for any given year, using Western, Orthodox or Julian algorithms;
    • A comprehensive test suite.

  • dateutil - powerful extensions to datetime — dateutil 2.6.1 documentation 抬頭寫著 "powerful extensions to datetime"，又 "Generic parsing of dates in almost any string format" 似乎是它的強項，另外也提供了 tzinfo 的實作。

  • python - How to parse an ISO 8601-formatted date? - Stack Overflow 由於 datetime.strptime() 不好用，許多人推薦用 python-dateutil 來解析字串。

跟 pytz 的關係?

dateutil 主要是用它的工具 (尤其是 parsing)，需要用到 timezone 時，習慣上還是會用 pytz。但 Python 3.6 之後似乎建議用 dateutil.tz?

參考資料：

新手上路 {: #getting-started }

  • dateutil - powerful extensions to datetime — dateutil 2.8.0 documentation

    • Suppose you want to know HOW MUCH TIME IS LEFT, in years/months/days/etc, before the next easter happening on a year with a Friday 13th in August, and you want to get today’s date out of the “date” unix system command. Here is the code:

      >>> from dateutil.relativedelta import *
>>> from dateutil.easter import *
>>> from dateutil.rrule import *
>>> from dateutil.parser import *
>>> from datetime import *
>>> now = parse("Sat Oct 11 17:13:46 UTC 2003")
>>> today = now.date()
>>> year = rrule(YEARLY,dtstart=now,bymonth=8,bymonthday=13,byweekday=FR)[0].year
>>> rdelta = relativedelta(easter(year), today)
>>> print("Today is: %s" % today)
Today is: 2003-10-11
>>> print("Year with next Aug 13th on a Friday is: %s" % year)
Year with next Aug 13th on a Friday is: 2004
>>> print("How far is the Easter of that year: %s" % rdelta)
How far is the Easter of that year: relativedelta(months=+6)
>>> print("And the Easter of that year is: %s" % (today+rdelta))
And the Easter of that year is: 2004-04-11

      範例有點難懂 ??

  • dateutil examples — dateutil 2.8.0 documentation #ril

  • Exercises — dateutil 2.8.0 documentation #ril

Parsing ??

  • parser — dateutil 2.8.0 documentation #ril

    • This module offers a GENERIC date/time string parser which is able to parse MOST KNOWN FORMATS to represent a date and/or time.

    • This module attempts to be FORGIVING with regards to unlikely input formats, returning a datetime object even for dates which are ambiguous. If an element of a date/time stamp is omitted, the following rules are applied:

      • If AM or PM is left unspecified, a 24-hour clock is assumed, however, an hour on a 12-hour clock (0 <= hour <= 12) must be specified if AM or PM is specified.

      • If a time zone is omitted, a timezone-NAIVE datetime is returned.

      • If any other elements are missing, they are taken from the datetime.datetime object passed to the parameter default.

        但為何 parser.parse('May 3') 會得到 datetime.datetime(2019, 5, 3, 0, 0)? 原來 dateutil.parser.parse 的實作 會拿當天的零時零分做為預設值：

        default = datetime.datetime.now().replace(hour=0, minute=0, second=0, microsecond=0)

        If this results in a day number exceeding the valid number of days per month, the value FALLS BACK TO THE END OF THE MONTH.

        但為何 parser.parse('Feb. 30') 會丟 ValueError: day is out of range for month 的錯誤 ??

    • Additional resources about date/time string formats can be found below:

  • parser — dateutil 2.6.1 documentation "This module offers a generic date/time string parser which is able to parse most known formats to represent a date and/or time."

安裝設置 {: #setup }

用 pip 安裝 python-dateutil 套件即可：(注意不是 dateutil)

pip install python-dateutil

參考資料 {: #reference }

手冊：