python笔记1-日期

1.显示当前日期和时间

from datetime import datetime

current_data = datetime.now()
print('today is: '+str(current_data))

从datetime库导入datetime，调用其中的now函数

print时要将日期类型强制转换为str，否则出现错误

    print('today is: '+current_data)
TypeError: can only concatenate str (not "datetime.datetime") to str

2.计算日期

from datetime import datetime,timedelta

# current_data = datetime.now()
# print('today is: '+str(current_data))

today = datetime.now()
print('today is: '+str(today))

one_day = timedelta(days=1)
yesterday = today - one_day
print('yesterday is: '+str(yesterday))

one_week =timedelta(weeks=1)
last_week = today - one_week
print('last week is: '+str(last_week))

这里计算了昨天和上周的日期

timedelta函数允许指定x天、x周等

30天/31天，是否闰年都可处理

3.单独显示日期部分

from datetime import datetime,timedelta

# current_data = datetime.now()
# print('today is: '+str(current_data))

today = datetime.now()
print('today is: '+str(today))

print('Day: '+str(today.day))
print('Month: '+str(today.month))
print('Year: '+str(today.year))

print('Hour: '+str(today.hour))
print('Minute: '+str(today.minute))
print('Second: '+str(today.second))

4.读取来自文件、数据库、用户所给的日期值

from datetime import datetime,timedelta

birthday = input('when is your birthday (dd/mm/yyyy)? ')

birthday_date = datetime.strptime(birthday,'%d/%m/%Y')
#strptime函数：按照指定格式解析字符串->指定格式日期类型（'%d/%m/%Y'）注意Y要大写
print('birthday is: '+str(birthday_date))

这些值在python中作为字符串（str）被读取，所以要转换成日期类型

同时，这些值的格式参差不齐，可能是日月年、月日年等，分割符可能是-、/......

待续