Day19.python时间和日期

雨点打透心脏的1/2处 2022-12-09 15:57 176阅读 0赞

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## Python时间和日期 ##

> **datetime模块**专门用于时间和日期的处理

常用的功能有以下几个：

### datetime.now()  &  datetime.today() ###

import datetime
     print(datetime.datetime.now())
     
     # datetime.today()
     #2020-09-21 23:13:05.245157
     print(datetime.datetime.today())
     #2020-09-21 23:13:57.062886

### datetime.strptime() ###

print(datetime.datetime.strptime('2020/08/09',format('%Y/%m/%d')))
     #2020-08-09 00:00:00
     print(datetime.datetime.strptime('20-08-09',format('%y-%m-%d')))
     #2020-08-09 00:00:00

### datetime.strftime() ###

接收以时间元组，并返回以可读字符串表示的当地时间，格式由参数format决定。

dt = datetime.datetime.now()  
     print("======================")
     print('时间：(%Y-%m-%d %H:%M:%S %f): ',dt.strftime( '%Y-%m-%d %H:%M:%S %f' ) )
     print('时间：(%Y-%m-%d %H:%M:%S %p): ' , dt.strftime( '%y-%m-%d %I:%M:%S %p' ) )
     print('星期缩写%%a: %s '  % dt.strftime( '%a' ))  
     print('星期全拼%%A: %s '  % dt.strftime( '%A' ))  
     print('月份缩写%%b: %s '  % dt.strftime( '%b' )  )
     print('月份全批%%B: %s '  % dt.strftime( '%B' ))  
     print('日期时间%%c: %s '  % dt.strftime( '%c' ) )
     print('今天是这周的第%s天 '  % dt.strftime( '%w' ) )
     print( '今天是今年的第%s天 '  % dt.strftime( '%j' ))  
     print('今周是今年的第%s周 '  % dt.strftime( '%U' ) )
     print('今天是当月的第%s天 '  % dt.strftime( '%d' ))
     
     '''
     ======================
     时间：(%Y-%m-%d %H:%M:%S %f):  2020-09-21 23:30:51 573645
     时间：(%Y-%m-%d %H:%M:%S %p):  20-09-21 11:30:51 PM
     星期缩写%a: Mon
     星期全拼%A: Monday
     月份缩写%b: Sep
     月份全批%B: September
     日期时间%c: Mon Sep 21 23:30:51 2020
     今天是这周的第1天
     今天是今年的第265天
     今周是今年的第38周
     今天是当月的第21天
     '''

## 时间日期的应用场景 ##

### 1.简介 ###

在编写代码时，往往涉及时间、日期、时间戳的相互转换。

### 2.示例 ###

# 引入模块
     import time, datetime

#### 2.1 str类型的日期转换为时间戳 ####

# 字符类型的时间
     
     testStr = '2020-09-21 23:26:33'
     
     # 转为 时间数组
     timeArray = time.strptime(testStr, "%Y-%m-%d %H:%M:%S")
     print(timeArray)
     
     # timeArray可以调用tm_year等
     print(timeArray.tm_year)  # 2020
     
     # 转为时间戳
     timeStamp = int(time.mktime(timeArray))
     print(timeStamp)  # 1600701993
     
     # 结果如下
     time.struct_time(tm_year=2020, tm_mon=9, tm_mday=21, tm_hour=23, tm_min=26, tm_sec=33, tm_wday=0, tm_yday=265, tm_isdst=-1)
     2020
     1600701993

#### 2.2 更改str类型日期的显示格式 ####

testStr1 = "2020-09-21 23:40:00"
     # 转为数组
     timeArray = time.strptime(testStr1, "%Y-%m-%d %H:%M:%S")
     # 转为其它显示格式
     otherStyleTime = time.strftime("%Y/%m/%d %H:%M:%S", timeArray)
     print (otherStyleTime)
     
     tss3 = "2020/09/21 23:40:00"
     timeArray = time.strptime(tss3, "%Y/%m/%d %H:%M:%S")
     otherStyleTime = time.strftime("%Y-%m-%d %H:%M:%S", timeArray)
     print (otherStyleTime)
     
     
     """
     -----------------------
     2020/09/21 23:40:00
     2020-09-21 23:40:00
     ======================
     
     """

#### 2.3 时间戳转换为指定格式的日期 ####

# 使用time
     timeStamp = 1600701993
     timeArray = time.localtime(timeStamp)
     otherStyleTime = time.strftime("%Y--%m--%d %H:%M:%S", timeArray)
     print(otherStyleTime)  # 2020--09--21 23:26:33
     # 使用datetime
     timeStamp = 1600101993
     dateArray = datetime.datetime.fromtimestamp(timeStamp)
     otherStyleTime = dateArray.strftime("%Y--%m--%d %H:%M:%S")
     print(otherStyleTime)  # 2020--09--15 00:46:33
     # 使用datetime，指定utc时间，相差8小时
     timeStamp = 1600201993
     dateArray = datetime.datetime.utcfromtimestamp(timeStamp)
     otherStyleTime = dateArray.strftime("%Y--%m--%d %H:%M:%S")
     print(otherStyleTime)  # 2020--09--15 20:33:13

#### 2.4 获取当前时间并且用指定格式显示 ####

print("+++++++++++++++++++++++++++++++++++++++++++")
     # time获取当前时间戳
     now = int(time.time())     # 1533952277
     timeArray = time.localtime(now)
     print (timeArray)
     otherStyleTime = time.strftime("%Y--%m--%d %H:%M:%S", timeArray)
     print (otherStyleTime)
     
     # 结果如下
     """
     time.struct_time(tm_year=2020, tm_mon=9, tm_mday=21, tm_hour=23, tm_min=45, tm_sec=53, tm_wday=0, tm_yday=265, tm_isdst=0)
     2020--09--21 23:45:53
     
     """
     
     
     # datetime获取当前时间，数组格式
     now = datetime.datetime.now()
     print (now)
     otherStyleTime = now.strftime("%Y--%m--%d %H:%M:%S")
     print (otherStyleTime)
     
     # 结果如下：
     
     """
     2020-09-21 23:45:53.543487
     2020--09--21 23:45:53
     """

## 日期函数 time模块函数 ##

这里说的字符串不是一般意义上的字符串，是指在读取日期类型的数据时，如果还没有及时解析字符串，它就还不是日期类型，那么此时的字符串该怎么与时间戳之间进行转换呢？

表示日期时间常用三种形式：

1.  秒为单位的浮点数
2.  struct\_time 元组
3.  时间字符串

import time;  # 引入time模块
     ticks = time.time()
     print ("当前时间戳为:", ticks)
     
     当前时间戳为: 1600704429.9781017

##### 秒为单位的浮点数 转换为 时间元组 #####

tm_struct = time.localtime(ticks)
     print(tm_struct)
     
     time.struct_time(tm_year=2020, tm_mon=9, tm_mday=22, tm_hour=0, tm_min=8, tm_sec=2, tm_wday=1, tm_yday=266, tm_isdst=0)

有时我们需要得到 格林威治时间，那么可以用**time.gmtime() 函数**：

#格林威治时间
     print(time.gmtime(ticks))
     
     
     time.struct_time(tm_year=2020, tm_mon=9, tm_mday=21, tm_hour=16, tm_min=9, tm_sec=18, tm_wday=0, tm_yday=265, tm_isdst=0)

##### 时间元组转换为秒为单位的浮点数 #####

print(time.mktime(tm_struct))
     
     1600704621.0

##### 时间元组转换为时间字符串 #####

转换方法有很多，最简单的是 **asctime():**

time_str = time.asctime( tm_struct )
     print(time_str)
     
     """
     Tue Sep 22 00:12:14 2020
     """

如果要精确控制格式，我们可以使用 **strftime():**

tm_1=time.strftime("%Y-%m-%d %H:%M:%S", tm_struct)
     tm_2=time.strftime("%a %b %d %H:%M:%S %Y", tm_struct)
     print(tm_1)
     print(tm_2)
     
     """
     2020-09-22 00:14:13
     Tue Sep 22 00:14:13 2020
     """

##### 时间字符串 转换为 时间元组 #####

函数 **time.strptime()** 可以完成这个转换，下面是个例子

tm2_struct = time.strptime('2020-09-22 01:34:50', "%Y-%m-%d %H:%M:%S")
     print(tm2_struct)
     
     """
     time.struct_time(tm_year=2020, tm_mon=9, tm_mday=22, tm_hour=1, tm_min=34, tm_sec=50, tm_wday=1, tm_yday=266, tm_isdst=-1)
     """

##### 秒为单位的浮点数 转换为 时间字符串 #####

**time.ctime()** 类似于 **time.asctime()**, 请看下面的例子：

tm_3=time.ctime(ticks)
     print(tm_3)
     
     """
     Tue Sep 22 00:17:54 2020
     
     """
     #如果想精确控制输出的字符串，我没查到有现成的函数。估计只能先转成元组，然后在格式化成字符串。
     #小编写了个转换函数：
     
     def time2str(ticks, fmt='%a %b %d %H:%M:%S %Y'):
         tm = time.localtime(ticks)
         return time.strftime(fmt, tm)

##### 时间字符串 转换为 秒为单位的浮点数 #####

def str2time(str, fmt='%a %b %d %H:%M:%S %Y')：
         tm = time.strptime(str, fmt)
         return time.mktime(tm)
     
     # 这里也是参考函数

--------------------

**作业练习**

## 根据起始和终止日期生成中间日期 ##

**pandas.to\_datetime**（*arg*，*errors ='raise'*，*utc = None*，*format = None*，*unit = None* ）将字符串转换为日期函数

#转换时间字符串格式，方法二：
     import pandas as pd
     start = pd.to_datetime("20200922")
     print("===================================")
     print(start)
     s=start.strftime('%Y-%m-%d') # 将datetime转为字符串，并以'%Y-%m-%d'格式输出
     print(s)
     print("===================================")
     
     """
     ==================================
     2020-09-22 00:00:00
     2020-09-22
     ==================================
     """

**编写函数：**

import time;  # 引入time模块
     from pandas import DatetimeIndex
     
     
     def date_range(cls, start=None, end=None, periods=None, freq=None, input_format=None, out_format=None):
         """
         生成时间序列
         :param start: 序列开始时间
         :param end: 序列结束时间, 给定start时, 结束时间包含end
         :param periods: int, 生成的时间序列长度
         :param freq: 要生成时间序列的时间间隔
         :param out_format: 是否输出格式化后的字符串, 若要输出可指定输出格式. "%Y-%m-%d %H:%M:%S"
         :param input_format: 若start或end是字符串且无法自动推断时间格式则需指定格式
         :return: [date or date_str]
     """
     
     start = pd.to_datetime("20200918")
     end = pd.to_datetime("20200922")
     pd.date_range(start, end)
     DatetimeIndex(['2020-09-28', '2020-09-29', '2020-09-30', '2020-09-13', '2020-06-01', '2020-06-02'])

**例题1：**

#例1：
     dates = ["20200912","20200922"]
     def create_dates(dates):
         """
         :param dates: ["20200912","20200922"]
         :return:
         """
         start = pd.to_datetime(dates[0])
         end = pd.to_datetime(dates[1])
         dates = pd.date_range(start, end)  # 生成时间字符串列表
         dates = dates.strftime('%Y%m%d')   #格式化时间数据
         return list(dates)
     
     print("例1")
     print(create_dates(dates))
     
     
     """
     例1
     ['20200912', '20200913', '20200914', '20200915', '20200916', '20200917', '20200918', '20200919', '20200920', '20200921', '20200922']
     
     """

**例题2：**

#例2
     
     df = pd.DataFrame({'year': [2019, 2020],
                            'month': [2, 3],
                            'day': [4, 5]})
     pd.to_datetime(df)
     
     print("例2")
     print(pd.to_datetime(df))
     
     
     """
     例2
     0   2019-02-04
     1   2020-03-05
     dtype: datetime64[ns]
     """

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