Python datetime module for time series

Public account: You and the cabin by: Peter Editor: Peter

Hello, I’m Peter

Peter introduced the Time module in detail in his previous Python time series article, and this article focuses on the DateTime module.

This module is an upgraded version of the Time module, with more common and comprehensive usage. Various examples will be provided to illustrate the use of this module.

Small talk

Recently, a lawyer added Peter through the public account. He learned Python in his spare time. Is this society really such a roll?

Friends, when it comes to Python, the best way to learn Python is to follow the example of Urhut

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Table of contents for reference:

Pandas articles

Pandas has been updated to article 26, with a recent focus on how to handle time series related data in Python or Pandas.

The last article is: Time module explanation, please refer to:

Datetime module

The main class

The main classes contained in the Datetime module are:

• Date: a date object. The commonly used attributes are year, month, and day
• Time: A time object. The main properties are hour, minute, second, and microsecond
• Datetime: a combination of date and datetime objects
• Datetime_CAPI: C interface for date objects
• Timedelta: Time interval between two times
• Tzinfo: Abstract base class for the time zone information object

constant

There are two constants:

1. MAXYEAR: Returns the maximum year that can be represented, datetime.MAXYEAR
2. MINYEAR: Returns the smallest year that can be represented, datetime.minyear

Five categories:

The following describes the specific use methods of the five categories in the Datetime module:

• date
• time
• datetime
• timedelta
• tzinfo

We must import the module before we can use it

from datetime import *   # * denotes all classes below the module
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The date class

Date object consists of year, year, month, and day.

The current time

Way # 1

from datetime import date

datetime.today().date()
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datetime.date(2021, 10, 20)
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Way # 2

from datetime import date

# today is a date object that returns the current date
today = date.today()
today  
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datetime.date(2021, 10, 20)
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Accessed by year, month, and day property descriptors:

print("This year:",today.year)   # return the year of the today object
print("This month:",today.month)  # return the month of the today object
print("Today:",today.day)   # return the day of the today object
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This year: 2021 This month: 10 Today: 20Copy the code

Through the.__getattribute__ (…). Method to obtain the above values:

today.__getattribute__("year")
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2021
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today.__getattribute__("month")
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10
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today.__getattribute__("day")
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20
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In addition, we can also access information about other date classes:

print("Current date:",today)  # current date
print("Current date (string) :",today.ctime())   # return a string of dates
print("Time (tuple) :",today.timetuple())   Time tuple information for the current date
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Current Date: 2021-10-20 Current date (string format) : Wed Oct 20 00:00:00 2021 time (tuple format) :  time.struct_time(tm_year=2021, tm_mon=10, tm_mday=20, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=2, tm_yday=293, tm_isdst=-1)Copy the code

print("This week:",today.weekday())  # 0 stands for Monday, and so on
print("Ordinal number of Gregorian calendar:",today.toordinal())  # return the ordinal number of the Gregorian calendar date
print(Year/week/week:,today.isocalendar())   # return a tuple: week of the year, day of the week
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Calendar Ordinal: 738083 years/Weeks/weeks: (2021, 42, 3)Copy the code

Custom time

Specify an arbitrary time:

# Customize a time

new_date = date(2021.12.8)  
new_date
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datetime.date(2021, 12, 8)
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# return different attributes

print("year: ", new_date.year)
print("month: ", new_date.month)
print("day: ", new_date.day)
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year:  2021
month:  12
day:  8
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# return time tuple
new_date.timetuple()
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time.struct_time(tm_year=2021, tm_mon=12, tm_mday=8, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=2, tm_yday=342, tm_isdst=-1)
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# return the Gregorian ordinal number

new_date.toordinal()
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738132
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# return week, 0 = 1,1 = 2

new_date.weekday()
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2
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# return week, 1 represents Monday, 1 represents Tuesday

new_date.isoweekday()
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3
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# return tuple :(year, week, day)

new_date.isocalendar()
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(2021, 49, 3)
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# Return date as a string in ISO 8601 format 'YYYY-MM-DD'

new_date.isoformat()
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'2021-12-08'
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# return a string of dates

new_date.ctime()
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'Wed Dec  8 00:00:00 2021'
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Specify different date output formats:

# returns a date string in the specified format

new_date.strftime("%Y-%m-%d")
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'2021-12-08'
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new_date.strftime("%Y/%m/%d")
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'2021/12/08'
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new_date.strftime("%Y %m %d")
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'08 December 2021'Copy the code

# replace time, for example we replace new_date

r_date = new_date.replace(2021.11.10)
r_date
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datetime.date(2021, 11, 10)
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In this case, we generate a new date object, and of course we can display the specified parameters:

new_date.replace(year=2021,month=11,day=11)
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datetime.date(2021, 11, 11)
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Gregorian calendar ordinal correlation

The ordinal is related to the toordinal method

# check the ordinal number of the current date

to_timestamp = today.toordinal()
to_timestamp
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738083
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Converts the given ordinal to a specific date and time: fromordinal

print(date.fromordinal(to_timestamp))
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2021-10-20
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Timestamp conversion

The conversion is done using the function fromtimestamp

import time
t = time.time()  The timestamp of the current time
t
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1634732660.382036
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print(date.fromtimestamp(t))  # timestamp --> date
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2021-10-20
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Convert arbitrary timestamps:

date.fromtimestamp(1698382719)
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datetime.date(2023, 10, 27)
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Time formatting

Let's format the output of the Today object

today
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datetime.date(2021, 10, 20)
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print(today.strftime("%Y/%m/%d"))
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2021/10/20
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print(today.strftime("%Y-%m-%d"))
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2021-10-20
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Time class

Create an object

Start by creating an arbitrary time

from datetime import time

t = time(20.30.40.1000)
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Accessing common properties

Hours, minutes and seconds are common attributes

print(t.hour)  When #
print(t.minute) # points
print(t.second)  # s
print(t.microsecond)  # microseconds
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20, 30, 40, 1000Copy the code

Formatted output

# return time string in ISO 8601 format

t.isoformat()
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'20:30:40. 001000'Copy the code

# specify the format of the output

t.strftime("%H:%M:%S:%f")
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'20:30:40:001000'
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Also, there is a replacement function:

# implicit substitution
t.replace(14.37.8)
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datetime.time(14, 37, 8, 1000)
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# explicit substitution

t.replace(hour=4,minute=18,second=19)
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datetime.time(4, 18, 19, 1000)
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Datetime class

A datetime object contains all information about a Date object and a time object. Summary of datetime-specific methods and attributes:

• The date (…). : Returns the date portion of a Datetime object
• Time (…). : Returns the time portion of a DateTime object
• Utctimetuple (…). : Returns the UTC time tuple part

Generate current date

from datetime import datetime 

k = datetime.today()  # Specify the current time
print(k)
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The 2021-10-20 20:24:23. 053493Copy the code

Access different attribute information for the current time:

print("year:",k.year)
print("month:",k.month)
print("day:",k.day)
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year: 2021
month: 10
day: 20
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Generate current time

# return the current time

n = datetime.now()
n
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datetime.datetime(2021, 10, 20, 20, 24, 23, 694127)
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Return the date portion of the datetime object

n.date()
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datetime.date(2021, 10, 20)
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Return the time portion of the dateTime object

n.time()
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datetime.time(20, 24, 23, 694127)
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Return the UTC tuple portion of the datetime object

n.utctimetuple()
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time.struct_time(tm_year=2021, tm_mon=10, tm_mday=20, tm_hour=20, tm_min=24, tm_sec=23, tm_wday=2, tm_yday=293, tm_isdst=0)
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Additional attribute information can also be generated:

# Return a datetime object for the current UTC date and time

print(datetime.utcnow())
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The 2021-10-20 12:24:24. 241577Copy the code

# Datetime object for the given timestamp

print(datetime.fromtimestamp(1697302830))  
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The 2023-10-15 01:00:30Copy the code

Datetime object that specifies the ordinal number of the Gregorian calendar

print(datetime.fromordinal(738000))Copy the code

2021-07-29 00:00:00
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# Concatenate date and time

print(datetime.combine(date(2020.12.25), time(11.22.54)))  
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The 2020-12-25 11:22:54Copy the code

Specify any time

# specify an arbitrary time

d = datetime(2021.9.25.11.24.23)
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print(d.date())  # date
print(d.time())  # time
print(d.timetz())  Split the time zone attribute from datetime

print(d.timetuple())  # time tuple
print(d.toordinal())  # Same as date.toordinal
print(d.weekday())  # Two weeks
print(d.isoweekday())
print(d.isocalendar())  ISO format output
print(d.isoformat())
print(d.strftime("%Y-%m-%d %H:%M:%S"))  # specify format
print(d.replace(year=2021,month=1))  # replace
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2021-09-25
11:24:23
11:24:23
time.struct_time(tm_year=2021, tm_mon=9, tm_mday=25, tm_hour=11, tm_min=24, tm_sec=23, tm_wday=5, tm_yday=268, tm_isdst=-1)
738058
5
6
(2021, 38, 6)
2021-09-25T11:24:23
2021-09-25 11:24:23
2021-01-25 11:24:23
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Formatted output

# Direct formatted output for time

print(datetime.strptime("2020-12-25"."%Y-%m-%d"))
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2020-12-25 00:00:00
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Formatted output for a given Datetime object, such as the instantiated object k created above:

k
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datetime.datetime(2021, 10, 20, 20, 24, 23, 53493)
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# format output

k.strftime("%Y-%m-%d %H:%M:%S")
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'the 2021-10-20 20:24:23'Copy the code

Timedelta class

The timedelta object represents a time period, the difference between two dates or datetimes.

Currently, the following parameters are supported :weeks, days, hours, minutes, seconds, milliseconds, and microseconds.

The current date

from datetime import timedelta, date, datetime

d = date.today()  # current date
d
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datetime.date(2021, 10, 20)
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print("Today:",d)
print("Plus 5 days:",d + timedelta(days=5))  # plus 5 days
print("Plus 3 days +8 hours:", d + timedelta(days=3,hours=8))  # Plus 3 days and 8 hours
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Today: 2021-10-20 plus 5 days: 2021-10-25 plus 3 days +8 hours: 2021-10-23Copy the code

Current point in time

# current point in time
now = datetime.now()  
now
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datetime.datetime(2021, 10, 20, 20, 24, 26, 777335)
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print(now + timedelta(hours=4))  # plus 4 hours
print(now + timedelta(weeks=2))  # plus 2 weeks
print(now - timedelta(seconds=500))  Minus 500 seconds
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2021-10-21 00:24:26.777335
2021-11-03 20:24:26.777335
2021-10-20 20:16:06.777335
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Datetime object difference

delta = datetime(2020.12.26) - datetime(2020.12.12.20.12)
print(delta)
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13 days, 3:48:00
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delta.days  # Date interval: days
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13
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delta.seconds  # Date interval: seconds
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13680
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delta.total_seconds()  # # Convert all to seconds
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1136880.0
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Two date differences

d1 = datetime(2021.10.1)
d2 = datetime(2021.10.8)
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d1.__sub__(d2)  # d1 - d2
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datetime.timedelta(days=-7)
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d2.__sub__(d1) # d2 - d1
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datetime.timedelta(days=7)
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# rsub means d2-d1

d1.__rsub__(d2)   
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datetime.timedelta(days=7)
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The difference between the two dates above results in datetime.timedelta. If the result is an integer, do as follows:

d1.__sub__(d2).days
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7 -Copy the code

Tzinfo classes

The time zone is specified

Specify the time zone

from datetime import date, timedelta, datetime, timezone

tz_utc_8 = timezone(timedelta(hours=8)) # create time zone
print(tz_utc_8)
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UTC+08:00
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now = datetime.now()
print(now)
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The 2021-10-20 20:24:28. 844732Copy the code

new_time = now.replace(tzinfo=tz_utc_8)  # Force plus 8 hours
print(new_time)
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The 2021-10-20 20:24:28. 844732 + 08:00Copy the code

Switching time zones

Get the UTC time
utc_now = datetime.utcnow().replace(tzinfo=timezone.utc)  # specify utc time zone
print(utc_now)
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The 2021-10-20 12:24:29. 336367 + 00:00Copy the code

# Switch to east 8 via astimeZone

beijing = utc_now.astimezone(timezone(timedelta(hours=8)))
print(beijing)
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The 2021-10-20 20:24:29. 336367 + 08:00Copy the code

Change the UTC time zone to East 9: Tokyo time

tokyo = utc_now.astimezone(timezone(timedelta(hours=9)))
print(tokyo)
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The 2021-10-20 21:24:29. 336367 + 09:00Copy the code

# Switch from Beijing time to Tokyo Time

tokyo_new = beijing.astimezone(timezone(timedelta(hours=9)))
print(tokyo_new)
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The 2021-10-20 21:24:29. 336367 + 09:00Copy the code

Common application

The timestamp is converted to a date

import time
now_timestamp = time.time()
now_timestamp
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1634732670.286224
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# 1- Switch to a specific point in time

now = time.ctime(now_timestamp)  
print(now)
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Wed Oct 20 20:24:30 2021
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# 2- The timestamp is converted to a time tuple before strftime is converted to the specified format

now_tuple = time.localtime(now_timestamp)
print(now_tuple)
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time.struct_time(tm_year=2021, tm_mon=10, tm_mday=20, tm_hour=20, tm_min=24, tm_sec=30, tm_wday=2, tm_yday=293, tm_isdst=0)
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time.strftime("%Y/%m/%d %H:%M:%S", now_tuple)
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'2021/10/20 20:24:30'
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# Select a specific timestamp

timestamp = 1618852721

a = time.localtime(timestamp)  Get time tuple form data
print("Time tuple data:",a)
time.strftime("%Y/%m/%d %H:%M:%S", a)  # format
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Time tuple data:  time.struct_time(tm_year=2021, tm_mon=4, tm_mday=20, tm_hour=1, tm_min=18, tm_sec=41, tm_wday=1, tm_yday=110, tm_isdst=0) '2021/04/20 01:18:41'Copy the code

time.ctime(1618852741)
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'Tue Apr 20 01:19:01 2021'
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Date time converts to timestamp

Given date data as a string, how do we convert it to the format we want?

date = "The 2021-10-26 11:45:34"

# 1. The time string is converted to the time array
date_array = time.strptime(date, "%Y-%m-%d %H:%M:%S")
date_array
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time.struct_time(tm_year=2021, tm_mon=10, tm_mday=26, tm_hour=11, tm_min=45, tm_sec=34, tm_wday=1, tm_yday=299, tm_isdst=-1)
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# 2, Check the time array data

print("Time array:", date_array)
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Time array:  time.struct_time(tm_year=2021, tm_mon=10, tm_mday=26, tm_hour=11, tm_min=45, tm_sec=34, tm_wday=1, tm_yday=299, tm_isdst=-1)Copy the code

# 3, mktime time array converted to timestamp

time.mktime(date_array)
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1635219934.0
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Date formatting

import time

old = "The 2021-09-12 12:28:45"

# 1. Convert to a time array
time_array = time.strptime(old, "%Y-%m-%d %H:%M:%S")

# 2, convert to new time format (2021/09/12 12-28-45)
new = time.strftime("%Y/%m/%d %H-%M-%S",time_array)  # specify the display format

print("Original format time:",old)
print("New format time:",new)
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Original format time: 2021-09-12 12:28:45 New format time: 2021/09/12 12-28-45Copy the code