python中的日期时间处理类——datetime

本文梳理了 python 中的日期时间处理类 datetime，记录了一些日常用法。

UTC#

What is UTC or GMT Time?

GMT: Greenwich Mean Time
UTC: Universal Time Coordinated

UTC – The World's Time Standard

UTC is A Standard, Not a Time Zone;
GMT is now a Time Zone.

Coordinated Universal Time (UTC, GMT, CUT)

时间服务器：

Epoch Converter：

datetime#

datetime

NAME
    datetime - Fast implementation of the datetime type.

CLASSES
    builtins.object
        date
            datetime
        time
        timedelta
        tzinfo
            timezone

class datetime.date

An idealized naive date, assuming the current Gregorian calendar always was, and always will be, in effect. Attributes: year, month, and day.

class datetime.time

An idealized time, independent of any particular day, assuming that every day has exactly 246060 seconds. (There is no notion of “leap seconds” here.) Attributes: hour, minute, second, microsecond, and tzinfo.

class datetime.datetime

A combination of a date and a time. Attributes: year, month, day, hour, minute, second, microsecond, and tzinfo.

class datetime.timedelta

A duration expressing the difference between two date, time, or datetime instances to microsecond resolution.

now & today#

调用 datetime.datetime 的 now() 或 today() 返回当前时间：

>>> dt_now = datetime.datetime.now()
>>> dt_now
datetime.datetime(2025, 11, 10, 22, 0, 35, 665900)

>>> dt_today = datetime.datetime.today()
>>> dt_today
datetime.datetime(2025, 11, 10, 22, 1, 10, 516142)

调用 datetime.date.today() 返回今日 datetime.date 对象：

>>> d_today = datetime.date.today()
>>> d_today
datetime.date(2025, 11, 10)

调用 datetime.datetime.combine() 方法，将 date 对象和 time 对象（默认构造零点）合并为 datetime 对象：

>>> dt_today = datetime.datetime.combine(d_today, datetime.time())
>>> dt_today
datetime.datetime(2025, 11, 10, 0, 0)

strftime#

strftime: Return a string representing the datetime/date

datetime.strftime(format)
date.strftime(format)

datetime 和 date 对象都支持 strftime() 方法，按格式输出日期字符串：

>>> import datetime

>>> datetime_now = datetime.datetime.now()
>>> datetime_now
datetime.datetime(2018, 4, 24, 15, 51, 2, 399371)
>>> datetime_now.strftime('%Y-%m-%d %H:%M:%S')
'2018-04-24 15:51:02'

type-specific formatting 等效写法：

>>> import datetime
>>> d=datetime.datetime(2018, 4, 25, 13, 0, 0)
>>> '{:%Y-%m-%d %H:%M:%S}'.format(d)
'2018-04-25 13:00:00'

strptime#

strptime: Return a datetime/date corresponding to date_string, parsed according to format.

classmethod datetime.strptime(date_string, format)
classmethod date.strptime(date_string, format)

datetime 和 date 对象都支持 strptime() 方法，从日期字符串按格式构造 datetime/date 对象：

>>> datetime_now = datetime.datetime.strptime('20180424', '%Y%m%d')
>>> datetime_begin = datetime.datetime.strptime('20180323', '%Y%m%d')
>>> datetime_count = datetime_now-datetime_begin
>>> datetime_count
datetime.timedelta(32)
>>> datetime_count.days
32

fromisoformat#

Return a datetime/date corresponding to a date_string in any valid ISO 8601 format.

classmethod datetime.fromisoformat(date_string)
classmethod date.fromisoformat(date_string)

datetime 和 date 对象都支持 fromisoformat() 方法，从日期字符串构造 datetime/date 对象：

>>> datetime.datetime.fromisoformat('2011-11-04')
datetime.datetime(2011, 11, 4, 0, 0)
>>> datetime.datetime.fromisoformat('20111104')
datetime.datetime(2011, 11, 4, 0, 0)
>>> datetime.datetime.fromisoformat('2011-11-04T00:05:23')
datetime.datetime(2011, 11, 4, 0, 5, 23)

>>> datetime.date.fromisoformat('2019-12-04')
datetime.date(2019, 12, 4)
>>> datetime.date.fromisoformat('20191204')
datetime.date(2019, 12, 4)

timestamp#

Unix 时间戳是从1970年1月1日（UTC/GMT的午夜）开始所经过的秒数（不考虑闰秒），是一个浮点数。
英文为 Unix time, POSIX time, Unix epoch 或 Unix timestamp。

The Current Epoch Unix Timestamp: Seconds since Jan 01 1970. (UTC)
The Unix epoch is the number of seconds that have elapsed since January 1, 1970 at midnight UTC time minus the leap seconds.

time和datetime都是Python中的内置模块，都可以对时间进行获取，对时间格式进行转换，如时间戳和时间字符串的相互转换。

Python中time和datetime时间戳和时间字符串相互转换

time#

time 模块定义的 time() 函数返回当前时间，是一个秒级时间戳浮点数。

FUNCTIONS

    time(...)
        time() -> floating point number

        Return the current time in seconds since the Epoch.

对于 time() 返回的秒级时间戳，乘以1000即可求得毫秒级：

import time, math

sTimestamp = time.time() # 6位小数
print(sTimestamp)
msTimestamp = time.time() * 1000
print(msTimestamp)
print(math.floor(msTimestamp)) # 向下取整，忽略us
print(round(msTimestamp)) # 四舍五入

运行输出：

1669000141.6891751
1669000141689.566
1669000141690
1669000141689

基于 time_ns() 接口返回高精度的纳秒级时间戳，来换算更粗粒度的毫秒单位，可能更为合理：

import time

sTimestamp = time.time() # 秒，6位小数
print(sTimestamp)
nsTimestamp = time.time_ns() # 纳秒
print(nsTimestamp)
msTimestamp = nsTimestamp / (1000 * 1000) # 毫秒
print(msTimestamp)

1669000543.659899
1669000543660408000
1669000543660.408

datetime#

class datetime 的实例方法 timestamp()：Return POSIX timestamp as float.

import datetime;

current_time = datetime.datetime.now()
time_stamp = current_time.timestamp()
print("timestamp:", time_stamp)

也可调用类方法 datetime.timestamp(dt)，其中dt为datetime对象实例：

from datetime import datetime

now = datetime.now()
timestamp = datetime.timestamp(now)
print("timestamp =", timestamp)

fromtimestamp#

classmethod datetime.fromtimestamp(timestamp, tz=None)
Return the local date and time corresponding to the POSIX timestamp, such as is returned by time.time().

也可调用类方法 datetime.timestamp(ts)，其中ts为秒级时间戳：

>>> datetime.fromtimestamp(time.time())
datetime.datetime(2022, 11, 21, 11, 42, 7, 720789)

timedelta#

>>> # 获取当前时间
>>> d0 = datetime.datetime.now()
>>> d0
datetime.datetime(2018, 4, 26, 22, 37, 55, 465668)
>>> # 基于日期字符串创建日期对象
>>> str_begin_date = '20180314'
>>> d1 = datetime.datetime.strptime(str_begin_date, '%Y%m%d')
>>> d2 = datetime.datetime(2018,2,2)
>>> # 计算日期相隔天数
>>> dd1=d0-d1
>>> dd1.days
43
>>> dd2=d1-d2
>>> dd2.days
40
>>> # 计算32天前的日期
>>> d3 = d0 - datetime.timedelta(days=32)
>>> d3
datetime.datetime(2018, 3, 25, 22, 37, 55, 465668)

假设有一个工单在明天过期，下面基于 datetime 来统计剩余天数。
由于现在不是今日零点，因此计算日期差不足 1 天：

>>> today = datetime.datetime.today()
>>> today
datetime.datetime(2018, 4, 26, 22, 37, 55, 465668)
>>> due_date = datetime.datetime.strptime('2018-04-27', '%Y-%m-%d')
>>> delta = due_date - today
>>> delta.days
0

如果要计算整点天数，需要取今日零点 datetime：

>>> d_today = datetime.date.today()  # datetime.datetime.today().date()
>>> dt_today = datetime.datetime.combine(d_today, datetime.time())
>>> dt_due = datetime.datetime.fromisoformat('2018-04-27')
>>> delta = dt_due - dt_today
>>> delta.days
1

基于 date 计算最合适：

>>> d_today = datetime.date.today()
>>> d_due = datetime.date.fromisoformat('2018-04-27')
>>> delta = d_due - d_today
>>> delta.days
1

python中的日期时间处理类——datetime

UTC#

datetime#

now & today#

strftime#

strptime#

fromisoformat#

timestamp#

time#

datetime#

fromtimestamp#

timedelta#

Examples#

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