462 lines
10 KiB
Markdown
462 lines
10 KiB
Markdown
# datetime模块
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datetime 是 Python 中处理日期的标准模块，它提供了 4 种对日期和时间进行处理的类：**datetime**、**date**、**time** 和 **timedelta**。
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---
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## 1. datetime类
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```python
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class datetime(date):
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def __init__(self, year, month, day, hour, minute, second, microsecond, tzinfo)
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pass
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def now(cls, tz=None):
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pass
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def timestamp(self):
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pass
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def fromtimestamp(cls, t, tz=None):
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pass
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def date(self):
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pass
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def time(self):
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pass
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def year(self):
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pass
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def month(self):
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pass
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def day(self):
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pass
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def hour(self):
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pass
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def minute(self):
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pass
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def second(self):
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pass
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def isoweekday(self):
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pass
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def strftime(self, fmt):
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pass
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def combine(cls, date, time, tzinfo=True):
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pass
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```
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- `datetime.now(tz=None)` 获取当前的日期时间，输出顺序为：年、月、日、时、分、秒、微秒。
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- `datetime.timestamp()` 获取以 1970年1月1日为起点记录的秒数。
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- `datetime.fromtimestamp(tz=None)` 使用 unixtimestamp 创建一个 datetime。
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【例子】如何创建一个 datetime 对象？
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```python
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import datetime
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dt = datetime.datetime(year=2020, month=6, day=25, hour=11, minute=23, second=59)
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print(dt) # 2020-06-25 11:23:59
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print(dt.timestamp()) # 1593055439.0
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dt = datetime.datetime.fromtimestamp(1593055439.0)
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print(dt) # 2020-06-25 11:23:59
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print(type(dt)) # <class 'datetime.datetime'>
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dt = datetime.datetime.now()
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print(dt) # 2020-06-25 11:11:03.877853
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print(type(dt)) # <class 'datetime.datetime'>
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```
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- `datetime.strftime(fmt)` 格式化 datetime 对象。
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符号 | 说明
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:---:|---
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`%a` | 本地简化星期名称（如星期一，返回 Mon）
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`%A` | 本地完整星期名称（如星期一，返回 Monday）
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`%b` | 本地简化的月份名称（如一月，返回 Jan）
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`%B` | 本地完整的月份名称（如一月，返回 January）
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`%c` | 本地相应的日期表示和时间表示
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`%d` | 月内中的一天（0-31）
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`%H` | 24小时制小时数（0-23）
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`%I` | 12小时制小时数（01-12）
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`%j` | 年内的一天（001-366）
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`%m` | 月份（01-12）
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`%M` | 分钟数（00-59）
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`%p` | 本地A.M.或P.M.的等价符
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`%S` | 秒（00-59）
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`%U` | 一年中的星期数（00-53）星期天为星期的开始
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`%w` | 星期（0-6），星期天为星期的开始
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`%W` | 一年中的星期数（00-53）星期一为星期的开始
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`%x` | 本地相应的日期表示
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`%X` | 本地相应的时间表示
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`%y` | 两位数的年份表示（00-99）
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`%Y` | 四位数的年份表示（0000-9999）
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`%Z` | 当前时区的名称（如果是本地时间，返回空字符串）
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`%%` | %号本身
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【例子】如何将 datetime 对象转换为任何格式的日期？
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```python
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import datetime
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dt = datetime.datetime(year=2020, month=6, day=25, hour=11, minute=51, second=49)
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s = dt.strftime("'%Y/%m/%d %H:%M:%S")
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print(s) # '2020/06/25 11:51:49
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s = dt.strftime('%d %B, %Y, %A')
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print(s) # 25 June, 2020, Thursday
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```
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【练习】如何将给定日期转换为 "mmm-dd, YYYY" 的格式？
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```python
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# 输入
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d1 = datetime.date('2010-09-28')
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# 输出
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'Sep-28,2010'
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```
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【参考答案】
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```python
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import datetime
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d1 = datetime.date(2010, 9, 28)
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print(d1.strftime('%b-%d,%Y'))
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# Sep-28,2010
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```
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- `datetime.date()` Return the date part.
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- `datetime.time()` Return the time part, with tzinfo None.
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- `datetime.year` 年
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- `datetime.month` 月
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- `datetime.day` 日
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- `datetime.hour` 小时
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- `datetime.minute` 分钟
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- `datetime.second` 秒
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- `datetime.isoweekday` 星期几
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【例子】datetime 对象包含很多与日期时间相关的实用功能。
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```python
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import datetime
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dt = datetime.datetime(year=2020, month=6, day=25, hour=11, minute=51, second=49)
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print(dt.date()) # 2020-06-25
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print(type(dt.date())) # <class 'datetime.date'>
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print(dt.time()) # 11:51:49
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print(type(dt.time())) # <class 'datetime.time'>
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print(dt.year) # 2020
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print(dt.month) # 6
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print(dt.day) # 25
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print(dt.hour) # 11
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print(dt.minute) # 51
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print(dt.second) # 49
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print(dt.isoweekday()) # 4
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```
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在处理含有字符串日期的数据集或表格时，我们需要一种自动解析字符串的方法，无论它是什么格式的，都可以将其转化为 datetime 对象。这时，就要使用到 dateutil 中的 parser 模块。
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- `parser.parse(timestr, parserinfo=None, **kwargs)`
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【例子】如何在 python 中将字符串解析为 datetime对象？
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```python
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from dateutil import parser
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s = '2020-06-25'
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dt = parser.parse(s)
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print(dt) # 2020-06-25 00:00:00
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print(type(dt)) # <class 'datetime.datetime'>
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s = 'March 31, 2010, 10:51pm'
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dt = parser.parse(s)
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print(dt) # 2010-03-31 22:51:00
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print(type(dt)) # <class 'datetime.datetime'>
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```
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【练习】如何将字符串日期解析为 datetime 对象？
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```python
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# 输入
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s1 = "2010 Jan 1"
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s2 = '31-1-2000'
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s3 = 'October10, 1996, 10:40pm'
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# 输出
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2010-01-01 00:00:00
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2000-01-31 00:00:00
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2019-10-10 22:40:00
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```
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【参考答案】
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```python
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from dateutil import parser
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s1 = "2010 Jan 1"
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s2 = '31-1-2000'
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s3 = 'October10, 1996, 10:40pm'
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dt1 = parser.parse(s1)
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dt2 = parser.parse(s2)
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dt3 = parser.parse(s3)
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print(dt1) # 2010-01-01 00:00:00
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print(dt2) # 2000-01-31 00:00:00
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print(dt3) # 1996-10-10 22:40:00
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```
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【练习】计算以下列表中连续的天数。
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```python
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# 输入
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['Oct, 2, 1869', 'Oct, 10, 1869', 'Oct, 15, 1869', 'Oct, 20, 1869','Oct, 23, 1869']
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# 输出
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[8, 5, 5, 3]
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```
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【参考答案】
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```python
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import numpy as np
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from dateutil import parser
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dateString = ['Oct, 2, 1869', 'Oct, 10, 1869', 'Oct, 15, 1869', 'Oct, 20, 1869', 'Oct, 23, 1869']
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dates = [parser.parse(i) for i in dateString]
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td = np.diff(dates)
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print(td)
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# [datetime.timedelta(days=8) datetime.timedelta(days=5)
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# datetime.timedelta(days=5) datetime.timedelta(days=3)]
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d = [i.days for i in td]
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print(d) # [8, 5, 5, 3]
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```
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---
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## 2. date类
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```python
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class date:
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def __init__(self, year, month, day):
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pass
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def today(cls):
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pass
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```
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- `date.today()` 获取当前日期信息。
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【例子】如何在 Python 中获取当前日期和时间？
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```python
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import datetime
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d = datetime.date(2020, 6, 25)
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print(d) # 2020-06-25
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print(type(d)) # <class 'datetime.date'>
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d = datetime.date.today()
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print(d) # 2020-06-25
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print(type(d)) # <class 'datetime.date'>
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```
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【练习】如何统计两个日期之间有多少个星期六？
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```python
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# 输入
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d1 = datetime.date(1869, 1, 2)
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d2 = datetime.date(1869, 10, 2)
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# 输出
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40
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```
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【参考答案】
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```python
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import datetime
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d1 = datetime.date(1869, 1, 2)
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d2 = datetime.date(1869, 10, 2)
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dt = (d2 - d1).days
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print(dt)
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print(d1.isoweekday()) # 6
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print(dt // 7 + 1) # 40
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```
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---
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## 3. time类
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```python
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class time:
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def __init__(self, hour, minute, second, microsecond, tzinfo):
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pass
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```
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【例子】如何使用 datetime.time() 类？
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```python
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import datetime
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t = datetime.time(12, 9, 23, 12980)
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print(t) # 12:09:23.012980
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print(type(t)) # <class 'datetime.time'>
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```
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注意：
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- 1秒 = 1000 毫秒（milliseconds）
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- 1毫秒 = 1000 微妙（microseconds）
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【练习】如何将给定日期转换为当天开始的时间？
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```python
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# 输入
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import datetime
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date = datetime.date(2019, 10, 2)
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# 输出
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2019-10-02 00:00:00
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```
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【参考答案】
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```python
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import datetime
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date = datetime.date(2019, 10, 2)
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dt = datetime.datetime(date.year, date.month, date.day)
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print(dt) # 2019-10-02 00:00:00
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dt = datetime.datetime.combine(date, datetime.time.min)
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print(dt) # 2019-10-02 00:00:00
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```
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---
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## 4. timedelta类
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`timedelta` 表示具体时间实例中的一段时间。你可以把它们简单想象成两个日期或时间之间的间隔。
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它常常被用来从 `datetime` 对象中添加或移除一段特定的时间。
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```python
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class timedelta(SupportsAbs[timedelta]):
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def __init__(self, days, seconds, microseconds, milliseconds, minutes, hours, weeks,):
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pass
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def days(self):
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pass
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def total_seconds(self):
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pass
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```
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【例子】如何使用 datetime.timedelta() 类？
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```python
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import datetime
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td = datetime.timedelta(days=30)
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print(td) # 30 days, 0:00:00
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print(type(td)) # <class 'datetime.timedelta'>
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print(datetime.date.today()) # 2020-07-01
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print(datetime.date.today() + td) # 2020-07-31
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dt1 = datetime.datetime(2020, 1, 31, 10, 10, 0)
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dt2 = datetime.datetime(2019, 1, 31, 10, 10, 0)
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td = dt1 - dt2
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print(td) # 365 days, 0:00:00
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print(type(td)) # <class 'datetime.timedelta'>
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td1 = datetime.timedelta(days=30) # 30 days
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td2 = datetime.timedelta(weeks=1) # 1 week
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td = td1 - td2
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print(td) # 23 days, 0:00:00
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print(type(td)) # <class 'datetime.timedelta'>
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```
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如果将两个 datetime 对象相减，就会得到表示该时间间隔的 timedelta 对象。
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同样地，将两个时间间隔相减，可以得到另一个 timedelta 对象。
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【练习】
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1. 距离你出生那天过去多少天了？
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2. 距离你今年的下一个生日还有多少天？
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3. 将距离你今年的下一个生日的天数转换为秒数。
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```python
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# 输入
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bday = 'Oct 2, 1969'
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```
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【参考答案】
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```python
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from dateutil import parser
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import datetime
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bDay = 'Oct 2, 1969'
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dt1 = parser.parse(bDay).date()
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dt2 = datetime.date.today()
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dt3 = datetime.date(dt2.year, dt1.month, dt1.day)
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print(dt1) # 1969-10-02
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print(dt2) # 2020-07-01
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print(dt3) # 2020-10-02
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td = dt2 - dt1
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print(td.days) # 18535
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td = dt3 - dt2
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print(td.days) # 93
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print(td.days * 24 * 60 * 60) # 8035200
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print(td.total_seconds()) # 8035200.0
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```
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---
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**练习题**：
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1、假设你获取了用户输入的日期和时间如`2020-1-21 9:01:30`，以及一个时区信息如`UTC+5:00`，均是`str`，请编写一个函数将其转换为timestamp：
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题目说明:
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```python
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"""
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Input file
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example1: dt_str='2020-6-1 08:10:30', tz_str='UTC+7:00'
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example2: dt_str='2020-5-31 16:10:30', tz_str='UTC-09:00'
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Output file
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result1: 1590973830.0
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result2: 1590973830.0
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"""
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def to_timestamp(dt_str, tz_str):
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# your code here
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pass
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```
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2、编写Python程序以选择指定年份的所有星期日。
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题目说明:
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```python
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"""
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Input file
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2020
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Output file
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2020-01-05
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2020-01-12
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2020-01-19
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2020-01-26
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2020-02-02
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-----
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2020-12-06
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2020-12-13
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2020-12-20
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2020-12-27
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"""
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def all_sundays(year):
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# your code here
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```
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