我们会经常遇到对时间的处理，用python来进行时间处理简直不要太方便了，这一期就给大家介绍一下python的时间处理！

用python进行时间处理主要会用到time,calendar,datetime及pandas这几个库,其中又以后两个最为常用。

这一期我们主要介绍一下用datetime库进行时间处理的常用操作。

1. datetime基础

1.1 获取当前时间

import time
import datetime as dtm
## 用datetime获取当前时间
dtime = dtm.datetime.now() # dtm.datetime.utcnow()
dtime
# datetime.datetime(2018, 12, 15, 13, 1, 30, 200649) # 年、月、日、时、分、秒、微秒
dtime.year, dtime.month, dtime.day
# (2018, 12, 15)
dtm.datetime.strftime(dtm.datetime.now(), '%y-%m-%d %h:%m:%s')
# '2018-12-15 20:47:45'
# 用time库获取当前时间：
time.strftime('%y-%m-%d %h:%m:%s', time.localtime(time.time( )))
# '2018-12-15 20:49:17'
time.strftime("%y-%m-%d %h:%m:%s")
# '2018-12-15 20:50:11'
1.2 datetime基本操作
from datetime import datetime, date, time
# using datetime.combine()
d = date(2005, 7, 14)
t = time(12, 30)
datetime.combine(d, t)
datetime(2005, 7, 14, 12, 30)
# datetime 类的方法：
datetime.date()
datetime.time()
# 可以用str()直接将时间格式转化为字符串
dt = datetime(2005, 7, 14, 12, 30)
# datetime(%y,%m,%d,%h,%m,%s):
# datetime共有6个参数，分别代表的是年月日时分秒。其中年月日是必须要传入的参数，时分秒可以不传入，默认全为零。
# >>> # using datetime.timetuple() to get tuple of all attributes
tt = dt.timetuple()
for it in tt:
print(it)
# 2005 # year
# 7 # month
# 14 # day
# 12 # hour
# 30 # minute
# 0 # second
# 3 # weekday (0 = monday, 6 = sunday)
# 195 # number of days since 1st january
# -1 # dst - method tzinfo.dst() returned none
####################################################
# 返回今天是周几
x='2018-05-27'
int(dtm.datetime(int(x[ :4]),int(x[5:7]),int(x[8: ])).strftime('%w'))
# 0 表示周日
dtm.datetime(2017, 1, 1).strftime("%w") # 0-6 sun-sat

2. 时间戳的转换

unix时间戳：  unix 中常常使用一个数字记录时间，表示距离起始时间相差的秒数(根据系统的精度，时间单位有时毫秒，有时是纳秒)。大于 0 表示在起始时间之后，小于 0 就表示在起始时间之前。这个数字有时是浮点类型、有时是整数类型，但都称这个数字为 unix 时间戳(timestamp)

import time
import datetime as dtm
## 获取当前时间
dtime = dtm.datetime.now() # dtm.datetime.utcnow()
# 时间戳
ans_time = int(time.mktime(dtime.timetuple()))
ans_time
# 1535860540
# 时间戳的转换-1
t1 = datetime.datetime.fromtimestamp(ans_time) # local time
t1
# datetime.datetime(2018, 9, 2, 11, 55, 40)
# 也可以用time模块的localtime()方法： time.localtime(ans_time)
# 时间戳的转换-2
t2 = datetime.datetime.utcfromtimestamp(ans_time) # utc time
t2
# datetime.datetime(2018, 9, 2, 3, 55, 40)
t2.strftime("%y--%m--%d %h:%m:%s")
# 2018--09--02 03:55:40
# 时间戳的转换-3
pd.to_datetime(ans_time,unit='s') # utc time
# timestamp('2018-09-02 03:55:40')

3. 时间格式的转换

strftime 即 string format time，用来将时间格式化成字符串
strptime 即 string parse time，用来将字符串解析成时间
import datetime as dtm
start = dtm.datetime(2011,1,7,1,21,1)
# datetime.datetime(2011, 1, 7, 1, 21, 1)
start.strftime('%y-%m-%d %h:%m:%s')
# '2011-01-07 01:21:01'
dtm.datetime.strptime('2011-01-07 01:21:01','%y-%m-%d %h:%m:%s')
# datetime.datetime(2011, 1, 7, 1, 21, 1)
str(start)
# '2011-01-07 01:21:01'
start.strftime("%y-%m-%d 00:00:00")
# '2011-01-07 00:00:00'
# the strftime method formats a datetime as a string:
in [1]: dt.strftime('%m/%d/%y %h:%m')
out[1]: '10/29/2011 20:30'
# strings can be converted (parsed) into datetime objects using the strptime function:
in [2]: dtm.datetime.strptime('20091031', '%y%m%d')
out[2]: datetime.datetime(2009, 10, 31, 0, 0)
>>> z
dtm.datetime(2012, 9, 23, 21, 37, 4, 177393)
>>> nice_z = dtm.datetime.strftime(z, '%a %b %d, %y')
>>> nice_z
'sunday september 23, 2012'
# 字符串形式的时间格式转化为时间格式
dt = dtm.datetime.strptime("21/11/06 16:30", "%d/%m/%y %h:%m")
# 时间格式转化为字符串
# time.strftime( '%y-%m-%d' , time.localtime(time.time()))
# >>> # formatting datetime
print(dt.strftime("%a, %d. %b %y %i:%m%p"))
# 'tuesday, 21. november 2006 04:30pm'
'the {1} is {0:%d}, the {2} is {0:%b}, the {3} is {0:%i:%m%p}.'.format(dt, "day", "month", "time")
# 'the day is 21, the month is november, the time is 04:30pm.'
'''
datetime format specification:
%y four-digit year
%y two-digit year
%m two-digit month [01, 12]
%d two-digit day [01, 31]
%h hour (24-hour clock) [00, 23]
%i hour (12-hour clock) [01, 12]
%m two-digit minute [00, 59]
%s second [00, 61] (seconds 60, 61 account for leap seconds)
%w weekday as integer [0 (sunday), 6]

datetime.strptime解析时间需要输入相应的时间格式，而dateutil第三方库中的parser.parse方法则更加灵活。

dateutil.parser 有时候也会有一定的麻烦，比如 '42'会被解析为2042 年加上今天的日期：datetime.datetime(2042, 9, 1, 0, 0)

from dateutil.parser import parse
parse('2011-01-03') # datetime.datetime(2011, 1, 3, 0, 0)
parse('jan 31, 1997 10:45 pm') # datetime.datetime(1997, 1, 31, 22, 45)
parse('6/12/2011', dayfirst=true) # datetime.datetime(2011, 12, 6, 0, 0)
# pandas:
datestrs = ['2011-07-06 12:00:00', '2011-08-06 00:00:00']
pd.to_datetime(datestrs)
# datetimeindex(['2011-07-06 12:00:00', '2011-08-06 00:00:00'], dtype='datetime64[ns]', freq=none)

4. timedelta

timedelta 可以表示两个时间之间的时间差：

dtm.timedelta(days=0, seconds=0, microseconds=0, milliseconds=0, minutes=0, hours=0, weeks=0)
t1 = dtm.datetime(2018,7,12,15,6,9)
t2 = dtm.datetime(2018,9,11,12,33,23)
td = t2-t1
td
# datetime.timedelta(60, 77234)
td.days,td.seconds
# (60, 77234)
# 将timedelta转换为: day, hour, minute
def parse_timedelta(td):
"""
transform timedelta to day, hour, minute
"""
return td.days, td.seconds//3600, (td.seconds//60)%60
parse_timedelta(td)
# (60, 21, 27)

利用timedelta进行时间外推：

import datetime as dtm
# 100天前的日期
(dtm.datetime.now() - dtm.timedelta(days = 100)).strftime("%y-%m-%d")
def taftd(format_date,i):
"""

返回几天后的时间

"""
return (dtm.datetime.strptime(format_date, '%y-%m-%d') + dtm.timedelta(days = i)).strftime('%y-%m-%d')
def tafth(format_time,i):
"""

返回几小时后的时间

"""
return (dtm.datetime.strptime(format_time, '%y-%m-%d %h:%m:%s') + dtm.timedelta(hours = i)).strftime('%y-%m-%d %h:%m:%s')
taftd("2018-05-17", -2)
# '2018-05-15'
tafth("2018-05-17 10:40:00", 2)
# '2018-05-17 12:40:00'

这一期主要介绍了是datetime进行时间处理的一些常用操作，后续我们会介绍pandas中的一些时间处理的操作。欢迎点赞转发期待哦~