python 日期、时间、字符串相互转换

在python中，日期类型date和日期时间类型dateTime是不能比较的。

（1）若是要比较，能够将dateTime转换为date，date不能直接转换为dateTime

import datetime
dateTime_p = datetime.datetime.now()  
date_p = dateTime_p.date() 
print(dateTime_p) #2019-01-30 15:17:46.573139
print(date_p) #2019-01-30

（2）日期类型date转换为字符串str

#!/usr/bin/env python3

import datetime
date_p = datetime.datetime.now().date()
str_p = str(date_p)
print(date_p,type(date_p)) #2019-01-30 <class 'datetime.date'>
print(str_p,type(str_p)) #2019-01-30 <class 'str'>

（3）字符串类型str转换为dateTime类型

import datetime
str_p = '2019-01-30 15:29:08'
dateTime_p = datetime.datetime.strptime(str_p,'%Y-%m-%d %H:%M:%S')
print(dateTime_p) # 2019-01-30 15:29:08

（4）dateTime类型转为str类型

　　这个地方我也不太理解，为何指定格式无效

import datetime
dateTime_p = datetime.datetime.now()
str_p = datetime.datetime.strftime(dateTime_p,'%Y-%m-%d')
print(dateTime_p) # 2019-01-30 15:36:19.415157

（5）字符串类型str转换为date类型

#!/usr/bin/env python3
import datetime
str_p = '2019-01-30'
date_p = datetime.datetime.strptime(str_p,'%Y-%m-%d').date()
print(date_p,type(date_p)) # 2019-01-30 <class 'datetime.date'>

另外dateTime类型和date类型能够直接作加1减1这种操做

#!/usr/bin/env python3
import datetime
# today = datetime.datetime.today()
today = datetime.datetime.today().date()
yestoday = today + datetime.timedelta(days=-1)
tomorrow = today + datetime.timedelta(days=1)
print(today) # 2019-01-30
print(yestoday)# 2019-01-29
print(tomorrow)# 2019-01-31