python的datetime

 

参考文章： https://www.programiz.com/python-programming/datetime

 

 

def get_days_count(start_date_time, end_date_time):
    '''
    得到2个时间之间的天数
    '''
    assert start_date_time is not None
    assert end_date_time is not None
    return (end_date_time - start_date_time).days

 

 

 

In this article, you will learn to manipulate date and time in Python with the help of examples.

Python has a module named datetime to work with dates and times. Let's create a few simple programs related to date and time before we dig deeper.

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Example 1: Get Current Date and Time

import datetime

datetime_object = datetime.datetime.now()
print(datetime_object)

When you run the program, the output will be something like:

2018-12-19 09:26:03.478039

Here, we have imported datetime module using import datetime statement.

One of the classes defined in the datetime module is datetime class. We then used now() method to create a datetime object containing the current local date and time.

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Example 2: Get Current Date

import datetime

date_object = datetime.date.today()
print(date_object)

When you run the program, the output will be something like:

2018-12-19

In this program, we have used today() method defined in the date class to get a date object containing the current local date.

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What's inside datetime?

We can use dir() function to get a list containing all attributes of a module.

import datetime

print(dir(datetime))

When you run the program, the output will be:

['MAXYEAR', 'MINYEAR', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', '_divide_and_round', 'date', 'datetime', 'datetime_CAPI', 'time', 'timedelta', 'timezone', 'tzinfo']

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Commonly used classes in the datetime module are:

• date Class
• time Class
• datetime Class
• timedelta Class

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datetime.date Class

You can instantiate date objects from the date class. A date object represents a date (year, month and day).

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Example 3: Date object to represent a date

import datetime

d = datetime.date(2019, 4, 13)
print(d)

When you run the program, the output will be:

2019-04-13

If you are wondering, date() in the above example is a constructor of the date class. The constructor takes three arguments: year, month and day.

The variable a is a date object.

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We can only import date class from the datetime module. Here's how:

from datetime import date

a = date(2019, 4, 13)
print(a)

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Example 4: Get current date

You can create a date object containing the current date by using a classmethod named today(). Here's how:

from datetime import date

today = date.today()

print("Current date =", today)

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Example 5: Get date from a timestamp

We can also create date objects from a timestamp. A Unix timestamp is the number of seconds between a particular date and January 1, 1970 at UTC. You can convert a timestamp to date using fromtimestamp() method.

from datetime import date

timestamp = date.fromtimestamp(1326244364)
print("Date =", timestamp)

When you run the program, the output will be:

Date = 2012-01-11

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Example 6: Print today's year, month and day

We can get year, month, day, day of the week etc. from the date object easily. Here's how:

from datetime import date

# date object of today's date
today = date.today() 

print("Current year:", today.year)
print("Current month:", today.month)
print("Current day:", today.day)

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datetime.time

A time object instantiated from the time class represents the local time.

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Example 7: Time object to represent time

from datetime import time

# time(hour = 0, minute = 0, second = 0)
a = time()
print("a =", a)

# time(hour, minute and second)
b = time(11, 34, 56)
print("b =", b)

# time(hour, minute and second)
c = time(hour = 11, minute = 34, second = 56)
print("c =", c)

# time(hour, minute, second, microsecond)
d = time(11, 34, 56, 234566)
print("d =", d)

When you run the program, the output will be:

a = 00:00:00
b = 11:34:56
c = 11:34:56
d = 11:34:56.234566

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Example 8: Print hour, minute, second and microsecond

Once you create a time object, you can easily print its attributes such as hour, minute etc.

from datetime import time

a = time(11, 34, 56)

print("hour =", a.hour)
print("minute =", a.minute)
print("second =", a.second)
print("microsecond =", a.microsecond)

When you run the example, the output will be:

hour = 11
minute = 34
second = 56
microsecond = 0

Notice that we haven't passed microsecond argument. Hence, its default value 0 is printed.

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datetime.datetime

The datetime module has a class named dateclass that can contain information from both date and time objects.

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Example 9: Python datetime object

from datetime import datetime

#datetime(year, month, day)
a = datetime(2018, 11, 28)
print(a)

# datetime(year, month, day, hour, minute, second, microsecond)
b = datetime(2017, 11, 28, 23, 55, 59, 342380)
print(b)

When you run the program, the output will be:

 

2018-11-28 00:00:00
2017-11-28 23:55:59.342380

The first three arguments year, month and day in the datetime() constructor are mandatory.

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Example 10: Print year, month, hour, minute and timestamp

from datetime import datetime

a = datetime(2017, 11, 28, 23, 55, 59, 342380)
print("year =", a.year)
print("month =", a.month)
print("hour =", a.hour)
print("minute =", a.minute)
print("timestamp =", a.timestamp())

When you run the program, the output will be:

year = 2017
month = 11
day = 28
hour = 23
minute = 55
timestamp = 1511913359.34238

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datetime.timedelta

A timedelta object represents the difference between two dates or times.

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Example 11: Difference between two dates and times

from datetime import datetime, date

t1 = date(year = 2018, month = 7, day = 12)
t2 = date(year = 2017, month = 12, day = 23)
t3 = t1 - t2
print("t3 =", t3)

t4 = datetime(year = 2018, month = 7, day = 12, hour = 7, minute = 9, second = 33)
t5 = datetime(year = 2019, month = 6, day = 10, hour = 5, minute = 55, second = 13)
t6 = t4 - t5
print("t6 =", t6)

print("type of t3 =", type(t3)) 
print("type of t6 =", type(t6))  

When you run the program, the output will be:

t3 = 201 days, 0:00:00
t6 = -333 days, 1:14:20
type of t3 = <class 'datetime.timedelta'>
type of t6 = <class 'datetime.timedelta'>

Notice, both t3 and t6 are of <class 'datetime.timedelta'> type.

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Example 12: Difference between two timedelta objects

from datetime import timedelta

t1 = timedelta(weeks = 2, days = 5, hours = 1, seconds = 33)
t2 = timedelta(days = 4, hours = 11, minutes = 4, seconds = 54)
t3 = t1 - t2

print("t3 =", t3)

When you run the program, the output will be:

t3 = 14 days, 13:55:39

Here, we have created two timedelta objects t1 and t2, and their difference is printed on the screen.

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Example 13: Printing negative timedelta object

from datetime import timedelta

t1 = timedelta(seconds = 33)
t2 = timedelta(seconds = 54)
t3 = t1 - t2

print("t3 =", t3)
print("t3 =", abs(t3))

When you run the program, the output will be:

t3 = -1 day, 23:59:39
t3 = 0:00:21

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Example 14: Time duration in seconds

You can get the total number of seconds in a timedelta object using total_seconds() method.

from datetime import timedelta

t = timedelta(days = 5, hours = 1, seconds = 33, microseconds = 233423)
print("total seconds =", t.total_seconds())

When you run the program, the output will be:

total seconds = 435633.233423

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You can also find sum of two dates and times using + operator. Also, you can multiply and divide a timedelta object by integers and floats.

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Python format datetime

The way date and time is represented may be different in different places, organizations etc. It's more common to use mm/dd/yyyy in the US, whereas dd/mm/yyyy is more common in the UK.

Python has strftime() and strptime() methods to handle this.

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Python strftime() - datetime object to string

The strftime() method is defined under classes date, datetime and time. The method creates a formatted string from a given date, datetime or time object.

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Example 15: Format date using strftime()

from datetime import datetime

# current date and time
now = datetime.now()

t = now.strftime("%H:%M:%S")
print("time:", t)

s1 = now.strftime("%m/%d/%Y, %H:%M:%S")
# mm/dd/YY H:M:S format
print("s1:", s1)

s2 = now.strftime("%d/%m/%Y, %H:%M:%S")
# dd/mm/YY H:M:S format
print("s2:", s2)

When you run the program, the output will be something like:

time: 04:34:52
s1: 12/26/2018, 04:34:52
s2: 26/12/2018, 04:34:52

Here, %Y, %m, %d, %H etc. are format codes. The strftime() method takes one or more format codes and returns a formatted string based on it.

In the above program, t, s1 and s2 are strings.

• %Y - year [0001,..., 2018, 2019,..., 9999]
• %m - month [01, 02, ..., 11, 12]
• %d - day [01, 02, ..., 30, 31]
• %H - hour [00, 01, ..., 22, 23
• %M - minute [00, 01, ..., 58, 59]
• %S - second [00, 01, ..., 58, 59]

To learn more about strftime() and format codes, visit: Python strftime().

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Python strptime() - string to datetime

The strptime() method creates a datetime object from a given string (representing date and time).

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Example 16: strptime()

from datetime import datetime

date_string = "21 June, 2018"
print("date_string =", date_string)

date_object = datetime.strptime(date_string, "%d %B, %Y")
print("date_object =", date_object)

When you run the program, the output will be:

date_string = 21 June, 2018
date_object = 2018-06-21 00:00:00

The strptime() method takes two arguments:

1. a string representing date and time
2. format code equivalent to the first argument

By the way, %d, %B and %Y format codes are used for day, month(full name) and year respectively.

Visit Python strptime() to learn more.

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Handling timezone in Python

Suppose, you are working on a project and need to display date and time based on their timezone. Rather than trying to handle timezone yourself, we suggest you to use a third-party pytZ module.

from datetime import datetime
import pytz

local = datetime.now()
print("Local:", local.strftime("%m/%d/%Y, %H:%M:%S"))


tz_NY = pytz.timezone('America/New_York') 
datetime_NY = datetime.now(tz_NY)
print("NY:", datetime_NY.strftime("%m/%d/%Y, %H:%M:%S"))

tz_London = pytz.timezone('Europe/London')
datetime_London = datetime.now(tz_London)
print("London:", datetime_London.strftime("%m/%d/%Y, %H:%M:%S"))

When you run the program, the output will be something like:

Local time: 2018-12-20 13:10:44.260462
America/New_York time: 2018-12-20 13:10:44.260462
Europe/London time: 2018-12-20 13:10:44.260462	

Here, datetime_NY and datetime_London are datetime objects containing the current date and time of their respective timezone.