python的datetime库

一、python对时间的定义

1.1 aware和naive

python doc里面有段这样的描述，将日期时间分为两种类型“aware”和“naive”。navie不携带timezone时区信息，所以navie的时间格式在理解上会有歧义。

Aware and Naive ObjectsDate and time objects may be categorized as “aware” or “naive” depending on whether or not they include timezone information. A naive object does not contain enough information to unambiguously locate itself relative to other date/time objects.

Python在这两个类型定义了3种日期时间格式

struct_time (naive)
POSIX (aware)
daattime (naive or aware)

因为naive无法感知时区信息，所以naive时间格式，按照使用习惯，我们会有naive local时区和naive UTC标准时区的分类。

进一步会分为这6种datetime：

struct_time (local)
struct_time (UTC)
POSIX (aware)
Aware datetime (进一步可分为Python2和Python3写法)
Navie datetime (local)
Navie datetime (UTC)

类型	写法
struct_time (local)	time.localtime()
struct_time (UTC)	time.gmtime()
POSIX	time.time()
Aware datetime (Python2)	datetime.datetime.now(pytz.timezone('UTC'))
Aware datetime (Python3)	datetime.datetime.now(datetime.timezone.utc)
Naive datetime (local)	datetime.datetime.now()
Naive datetime (UTC)	datetime.datetime.utcnow()

注意到Aware datetime (Python2) 的写法，因为Python2的datetime缺少timezone，所以需要安装第三方库来支持。

代码语言：bash复制

python2 -m pip install pytz tzlocal

1.2 struct_time和POXIS时间戳

struct_time和POSIX时间戳的表达如下：

代码语言：python代码运行次数：0复制

import os,time

os.environ['TZ'] = 'Asia/Shanghai'
time.tzset()

print(time.localtime())  # struct time(local)
print(time.gmtime()) # struct time(UTC)
print(time.time())  # POSIX

1.3 datetime

接下来看下datetime库是怎么表达时间的。

代码语言：python代码运行次数：0复制

import os,time

os.environ['TZ'] = 'Asia/Shanghai'
time.tzset()

import datetime

print(datetime.datetime.now(datetime.timezone.utc))  # Aware datetime(Python3)
print(datetime.datetime.now()) # Naive datetime(local)
print(datetime.datetime.utcnow())  # Naive datetime(UTC)

二、使用datetime库

datetime提供的常用操作包括：

2.1 datetime对象的序列化和反序列化

datetime有两个函数：strptime用来将日期字符串反序列化成datetime对象；strftime用来按照一定的格式序列化生成日期字符串。

举例来说：

代码语言：python代码运行次数：0复制

from datetime import datetime

data = datetime.strptime("2024-1-21_22:01:02", "%Y-%m-%d_%H:%M:%S")

print(data.strftime("%Y%m%d %H:%M:%S"))
print(datetime.now().strftime("%Y-%m-%d_%H:%M:%S"))

2.2 获取当前时间

代码语言：python代码运行次数：0复制

from datetime import datetime

print(datetime.now())
print(datetime.now().isoformat())
print(datetime.now().isocalendar())
print(datetime.today())
print(datetime(2024, 1, 21, 22, 1, 2, 100999))
print(datetime.date(*map(int, "2024-1-21".split('-'))))

2.3 时间运算

代码语言：python代码运行次数：0复制

from datetime import datetime,timedelta

print(datetime.today())
print(datetime.today()   timedelta(days=1))

2.4 时区

代码语言：python代码运行次数：0复制

from datetime import datetime,timedelta,timezone

print(datetime.today())
print(datetime.today().replace(tzinfo=timezone.utc))
print(datetime.today().replace(tzinfo=timezone(timedelta(hours=8))))

三、各种time类型的互相转换

Row -> Col	POSIX	struct_time(local)	struct_time(UTC)	Naive datetime(local)	Naive datetime(UTC)	Aware datetime(Py2)	Aware datetime(Py3)
POSIX	-	time.localtime(x)	time.gmtime(x)	datetime.datetime.fromtimestamp(x)	datetime.datetime.fromtimestamp(x)	datetime.datetime.fromtimestamp(x,pytz.timezone('UTC'))	datetime.datetime.fromtimestamp(x,datetime.timezone.utc)
struct_time(local)	time.mktime(x)	-	-	datetime.datetime(*x[:6])	-	-	-
struct_time(UTC)	calendar.timegm(x)	-	-	-	datetime.datetime(*x[:6])	datetime.datetime(*x[:6], tzinfo=pytz.timezone('UTC'))	datetime.datetime(*x[:6], tzinfo=datetime.timezone.utc)
Naive datetime(local)	-	-	-	-	-	x.replace(tzinfo=tzlocal.get_local_zone())	x.astimezone()
Naive datetime(UTC)	calendar.timegm(x.utctimetupe())	-	x.utctimetupe()	-	-	x.replace(tzinfo=pytz.timezone('UTC'))	x.replace(tzinfo=pytz.timezone.utc)
Aware datetime(Py2)	calendar.timegm(x.utctimetupe())	-	x.utctimetupe()	x.astimezone(tzlocal.get_localzone()).replace(tzinfo=None)	x.astimezone(pytz.timezone('UTC')).replace(tzinfo=None)	-	-
Aware datetime(Py3)	calendar.timegm(x.utctimetupe())	-	x.utctimetupe()	x.astimezone().replace(tzinfo=None)	x.astimezone(pytz.timezone.utc).replace(tzinfo=None)	-	-

python datetime time

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