datetime 모듈

• datetime 클래스
  weekday()
  0:월, 1:화, 2:수, 3:목, 4:금, 5:토, 6:일
  ```python

  from datetime import datetime
  cur = datetime.now()
  cur
  datetime.datetime(2019, 5, 4, 17, 51, 56, 408364)
  cur.year
  2019
  cur.month
  5
  cur.day
  4
  cur.hour
  17
  cur.minute
  51
  cur.second
  56
  cur.microsecond
  408364
  cur.weekday()
  5
  cur.strftime("%Y/%m/%d %H:%M:%S %A %B")
  '2019/05/04 17:51:56 Saturday May'
  cur.date()
  datetime.date(2019, 5, 4)
  cur.time()
  datetime.time(17, 51, 56, 408364)

* timedelta 클래스
날짜/시간 연산
    * total_seconds()
    모든 속성을 초.마이크로초로 반환
	* ```python
>>> start = datetime.now()
>>> end = datetime.now()
>>> elpsed = end - start
>>> elpsed
datetime.timedelta(0, 9, 121426)
>>> elpsed.days, elpsed.seconds, elpsed.microseconds
(0, 9, 121426)
>>> elpsed.total_seconds()
9.121426
>>> from datetime import timedelta
>>> datetime(2019, 5, 4) + timedelta(days=10)
datetime.datetime(2019, 5, 14, 0, 0)

dateutil

• 설치 pip install python-dateutil
• function parse
  자동으로 형식 문자열을 찾아 datetime.datetime 클래스 객체를 만들어 준다.
  월, 일
  월과 일이 모두 12보다 작으면 먼저 나오는 숫자를 월로 판단한다.
  12보다 큰 숫자를 일로 판단한다.
  ```python

  from dateutil.parser import parse
  parse('2016-04-16')
  datetime.datetime(2016, 4, 16, 0, 0)
  parse('2019-05-04 18:03:11')
  datetime.datetime(2019, 5, 4, 18, 3, 11)
  parse("Apr 16, 2016 04:05:32 PM")
  datetime.datetime(2016, 4, 16, 16, 5, 32)
  parse('6/7/2016')
  datetime.datetime(2016, 6, 7, 0, 0)
  parse('16/7/2016')
  datetime.datetime(2016, 7, 16, 0, 0)

* class relativedelta
년(year), 월(month) 더하고 빼기
	* ```python
>>> from dateutil.relativedelta import relativedelta
>>> from datetime import datetime
>>> datetime.now()
datetime.datetime(2019, 5, 4, 18, 5, 23, 624826)
>>> datetime.now() - relativedelta(years=1)
datetime.datetime(2018, 5, 4, 18, 5, 31, 567166)
>>> datetime.now() + relativedelta(years=1)
datetime.datetime(2020, 5, 4, 18, 5, 45, 334084)
>>> datetime.now() - relativedelta(months=3)
datetime.datetime(2019, 2, 4, 18, 5, 51, 619240)
>>> datetime.now() + relativedelta(months=3)
datetime.datetime(2019, 8, 4, 18, 5, 58, 367941)
>>> datetime.now() + relativedelta(days=5)
datetime.datetime(2019, 5, 9, 18, 9, 37, 71110)

• rrule 클래스
  두 날짜의 년, 월 수 구하기
  * ```python

  from dateutil import rrule
  from datetime import date
  dir(rrule)
  ['DAILY', 'FR', 'FREQNAMES', 'HOURLY', 'M365MASK', 'M365RANGE', 'M366MASK', 'M366RANGE', 'MDAY365MASK', 'MDAY366MASK', 'MINUTELY', 'MO', 'MONTHLY', 'NMDAY365MASK', 'NMDAY366MASK', 'SA', 'SECONDLY', 'SU', 'TH', 'TU', 'WDAYMASK', 'WE', 'WEEKLY', 'YEARLY', 'all', 'builtins', 'cached', 'doc', 'file', 'loader', 'name', 'package', 'spec', '_invalidates_cache', '_iterinfo', '_rrulestr', '_thread', 'advance_iterator', 'calendar', 'datetime', 'easter', 'gcd', 'heapq', 'integer_types', 'itertools', 'parser', 'range', 'rrule', 'rrulebase', 'rruleset', 'rrulestr', 'sys', 'warn', 'weekday', 'weekdaybase', 'weekdays']
  diff_months_list = list(rrule.rrule(rrule.MONTHLY, dtstart=date(2016, 10, 1), until=date(2017, 5, 15)))
  diff_months_list
  [datetime.datetime(2016, 10, 1, 0, 0), datetime.datetime(2016, 11, 1, 0, 0), datetime.datetime(2016, 12, 1, 0, 0), datetime.datetime(2017, 1, 1, 0, 0), datetime.datetime(2017, 2, 1, 0, 0), datetime.datetime(2017, 3, 1, 0, 0), datetime.datetime(2017, 4, 1, 0, 0), datetime.datetime(2017, 5, 1, 0, 0)]
  len(diff_months_list)
  8
  diff_years_list = list(rrule.rrule(rrule.YEARLY, dtstart=date(2016, 10, 1), until=date(2020, 5, 15)))
  diff_years_list
  [datetime.datetime(2016, 10, 1, 0, 0), datetime.datetime(2017, 10, 1, 0, 0), datetime.datetime(2018, 10, 1, 0, 0), datetime.datetime(2019, 10, 1, 0, 0)]
  len(diff_years_list)
  4

# calendar 모듈
* function calendar.monthrange(year, month)
	* tuple을 리턴
		* 첫 번째 원소는 month의 1일이 무슨 요일인지(0:월, 1:화...,) 
		* 두 번째 원소는 month가 총 며칠 인지
	* ```python
>>> import calendar
>>> calendar.monthrange(2019, 3)
(4, 31)
>>> calendar.monthrange(2019, 4)
(0, 30)