13장 Calendars and Clocks

Table of contents

1. Leap Year(윤년)
2. The datetime Module
3. Using the time Module
4. Read and Write Dates and Times
5. All the Conversions
6. Alternative Modules
7. Coming Up
8. Things to Do

Python’s standard library has many date and time modules, including: datetime, time, calendar, dateutil, and others.

Leap Year(윤년)

윤년은 특정한 시간 주기다.

>>> import calendar
>>> calendar.isleap(1900)
False
>>> calendar.isleap(1996)
True
>>> calendar.isleap(1999)
False
>>> calendar.isleap(2000)
True
>>> calendar.isleap(2002)
False
>>> calendar.isleap(2004)
True

For the curious:

• A year has 365.242196 days (after one spin around the sun, the earth is about a quarter-turn on its axis from where it started).
• Add one day every four years. Now an average year has 365.242196 – 0.25 = 364.992196 days
• Subtract a day every 100 years. Now an average year has 364.992196 + 0.01 = 365.002196 days
• Add a day every 400 years. Now an average year has 365.002196 – 0.0025 = 364.999696 days

Close enough for now! We will not speak of leap seconds.

The datetime Module

The standard datetime module handles (which should not be a surprise) dates and times. It defines four main object classes, each with many methods:

• date : years, months, and days
• time : hours, minutes, seconds, and fractions
• datetime : dates, times
• timedelta : date and/or time intervals

You can make a date object by specifying a year, month, and day. Those values are then available as attributes:

from datetime import date
halloween = date(2019, 10, 31)
print(halloween) # datetime.date(2019, 10, 31)
print(halloween.day) # 31

now = date.today()
print(now)         # 오늘 날짜 출력

from datetime import *
delta = timedelta(days=1)
now = datetime.now()
tomorrow = now + delta
print('now : %s, tomorrow : %s'%(now,tomorrow))
print(now + 17*delta)  # 17일 후

# 타임 다루기
from datetime import time
noon = time(12, 0, 0)
print(noon) # datetime.time(12, 0)
print(noon.hour) # 12

from datetime import datetime
some_day = datetime(2019, 1, 2, 3, 4, 5, 6) #마지막인수 - 마이크로초
print(some_day)  # datetime.datetime(2019, 1, 2, 3, 4, 5, 6)
iso = some_day.isoformat()  # datetime자료형 -> 인식 가능 하게
print(iso) # 2019-01-02T03:04:05.000006

now = datetime.now()
print(now)  # 2022-12-30 22:09:49.004540
print(now.year) # 2022

d = some_day.date() # date부분만 추출
print(d)            # 2019-01-02
s = some_day.time() # time부분만 추출
print(s) # 03:04:05.000006

con = datetime.combine(d,s) # date, time -> datetime으로
print(con)                  # 2019-01-02 03:04:05.000006

Using the time Module

유닉스 계열의 시간 개념 (다른 시스템과 교환 가능): 1970/1/1 자정 이후의 초를 사용한다 - epoch값

The time module’s time() function returns the current time as an epoch value:

>>> import time
>>> now = time.time()
>>> now
1554512132.778233
>>> time.ctime(now)
'Fri Apr 5 19:55:32 2019'

import time

now = time.time()
t = time.localtime()  # 현시간 표준시
t1 = time.gmtime()    # 현시간 UTC(절대시간)
print(now)
print(t)
print(t1)
'''
1674095102.1614609
time.struct_time(tm_year=2023, tm_mon=1, tm_mday=19, tm_hour=11, tm_min=25, tm_sec=2, tm_wday=3, tm_yday=19, tm_isdst=0)    
time.struct_time(tm_year=2023, tm_mon=1, tm_mday=19, tm_hour=2, tm_min=25, tm_sec=2, tm_wday=3, tm_yday=19, tm_isdst=0)     

'''

Table 13-1. struct_time values

Read and Write Dates and Times

You can also convert dates and times to strings by using strftime(). This is provided as a method in the datetime, date, and time objects, and as a function in the time module. strftime() uses format strings to specify the output, which you can see in Table 13-2.

Table 13-2. Output specifiers for strftime()

• localtime -> 포멧된 time

import time
fmt = "It's %A, %B %d, %Y, local time %I:%M:%S%p"
t = time.localtime()

s = time.strftime(fmt, t)
print(s) # "It's Wednesday, March 13, 2019, local time 03:23:46PM"

• date객체 -> 포멧된 time

from datetime import date
some_day = date(2019, 7, 4)
fmt = "It's %A, %B %d, %Y, local time %I:%M:%S%p"
s = some_day.strftime(fmt)
print(s) # "It's Thursday, July 04, 2019, local time 12:00:00AM"

• time객체 -> 포멧된 time

from datetime import time
fmt = "It's %A, %B %d, %Y, local time %I:%M:%S%p"
some_time = time(10, 35)
s=some_time.strftime(fmt)
print(s) # "It's Monday, January 01, 1900, local time 10:35:00AM"

• 문자열 -> struct_time

  import time
  fmt = "%Y-%m-%d"
  s = time.strptime("2019-01-29", fmt)
  print(s) # time.struct_time(tm_year=2019, tm_mon=1, tm_mday=29, tm_hour=0,tm_min=0, tm_sec=0, tm_wday=1, tm_yday=29, tm_isdst=-1)
  

Names are specific to your locale—internationalization settings for your operating system. If you need to print different month and day names, change your locale by using setlocale(); its first argument is locale.LC_TIME for dates and times, and the second is a string combining the language and country abbreviation. Let’s invite some

international friends to a Halloween party. We’ll print the month, day, and day of week in US English, French, German, Spanish, and Icelandic (Icelanders have real elves):

import locale
from datetime import date
halloween = date(2019, 10, 31)
for lang_country in ['en_us', 'fr_fr', 'de_de', 'es_es', 'is_is','ko-ko']:
    s = locale.setlocale(locale.LC_TIME, lang_country)
    print(s)
    s1 = halloween.strftime('%A, %B %d')
    print(s1.encode('utf-8', 'replace').decode())

'''
Thursday, October 31
jeudi, octobre 31
Donnerstag, Oktober 31
jueves, octubre 31
fimmtudagur, okt?ber 31
jeudi, octobre 31
de_de
Donnerstag, Oktober 31
es_es
jueves, octubre 31
is_is
fimmtudagur, október 31
ko-ko
목요일, 10월 31
'''

# 국가코드 확인 : dict형식
names = locale.locale_alias
print(names)

All the Conversions

Figure 13-1 (from the Python wiki) summarizes all the standard Python time inter‐

conversions.

Figure 13-1. Date and time conversions

Alternative Modules

• arrow : Combines many date and time functions with a simple API

• dateutil : Parses almost any date format and handles relative dates and times well

• iso8601 : Fills in gaps in the standard library for the ISO8601 format

• fleming : Many time zone functions

• maya : Intuitive interface to dates, times, and intervals

• dateinfer : Guesses the right format strings from date/time strings

Coming Up

Files and directories need love, too.

Things to Do

13.1 Write the current date as a string to the text file today.txt.

13.2 Read the text file today.txt into the string today_string.

13.3 Parse the date from today_string.

13.4 Create a date object of your day of birth.

13.5 What day of the week was your day of birth?

13.6 When will you be (or when were you) 10,000 days old?