An essential aspect of any program in python is datetime. Python provides the python datetime module that helps manipulate date and time and represents it in a way users can understand. When you talk about datetime, there are various components to it. The datetime module consists of the following object types:

• date -holds the date
• time -holds the time
• datetime -holds both date and time

###How to Get Current Date and Time

As you have seen above, the Python datetime module is available to do this. Import the datetime class form the datetime module then use it to create a datetime object, as shown below. Python datetime module provides the now() method from the datetime class, which gives us the local date and time.

import datetime
dt_object = datetime.datetime.now()
print(dt_object)

The result is:

2019-10-17 16:13:43.300953

Get the Current Date in Python

You use the Python date class to create or modify date objects. For example, to get the local date:

from datetime import date
current_date = date.today()
print(current_date)

The result is:

2019-10-17

The current date is 2019, 10, 17 in the format( year, month, day), respectively.

Get the Current Time in Python

To get the current/local time, you first obtain the current date and time and then break it into time by calling the time() method

import datetime
local_date_time = datetime.datetime.now()
local_time = local_date_time.time()
print(local_time)

The result is :

16:19:48.809945

Components of Python Datetime

The Python datetime module can be used to obtain different versions of time. Let''s look at the attributes in the datetime module. To do that, you are going to use the dir() function.

import datetime
attr = dir(datetime)
attr
['MAXYEAR', 'MINYEAR', '__doc__', '__name__', '__package__', 'date', 'datetime', 'datetime_CAPI', 'time', 'timedelta', 'tzinfo']

In this tutorial, you''ll cover the following attributes:

• date - These are date objects
• datetime - these are both date and time objects
• time - these are time objects
• timedelta -this attribute covers intervals in time and is used to determine past and future dates
• Tzinfo - this attribute deals with timezones

How to Create Date and Time Objects

To create a time object, you use the time class from the Python datetime module, and the syntax is: datetime.time(hour, minutes, seconds). In the code below, create a time object which is represented by (8,48,45)

import datetime
timeobj= datetime.time(8,48,45)
print(timeobj)

The result is:

08:48:45

You first import the datetime module, then create an instance of the time class (which is a time object). You then set it equal to datetime.time(8,48,45), where the parameters 8,48,45 represents the hour, and seconds respectively.

To create a date object, pass the desired date in the following syntax:

datetime.datetime(year,month,day))

Consider the following example.

import datetime;  
date_object = datetime.datetime(2019,10,17)
print(date_object)

The result is:

2019-10-17 00:00:00

Timedelta

Timedelta represents a duration, i.e., a duration of date or time. Python datetime module contains the timedelta() attribute, which is used to perform date manipulations in python. A timedelta object is represented as follows:

td_object =timedelta(days=0, seconds=0, microseconds=0, milliseconds=0, minutes=0, hours=0, weeks=0)
td_object
datetime.timedelta(0)

NB All arguments are optional and default to 0 and can be floats, integers, positives, or negatives. You can be able to perform mathematical operations such as addition, subtraction, and multiplication with the timedelta class.

How to Calculate the Time Difference Between Two Dates

Let''s look at some examples of how to get the time difference. Let's say you have two datetime. date objects as shown below

first_date = date(2019, 10, 2)
second_date = date(2014, 10, 30)

To obtain the difference, subtract the two dates as follows

from datetime import date
first_date = date(2019, 10, 2)
second_date = date(2019, 10, 30)
delta = second_date - first_date
print(delta)

The result is:

28 days,0:00:00

Therefore the number of days between 2nd October 2019 and 30th October 2019 is 28 days.

How to Calculate the Time Difference Between Two datetime.time Objects

You cannot perform manipulations of time objects with timedelta and the following code results in an error.

from datetime import datetime, timedelta

current_datetime = datetime.now()
current_time = current_datetime.time()
print('Current Time:', current_time)
tm_after_1_hr = current_time + timedelta(hours=1)
print(tm_after_1_hr)

So the error will be:

python tTypeError: unsupported operand type(s) for +: 'datetime.time' and 'datetime.timedelta'

How to Get Past and Future Dates With Timedelta

Since timedelta represents a duration, to get any future or past date, you add or subtract timedelta to the current date, respectively. A simple equation to show this is.

import datetime
current_date = datetime.datetime.today()
past_date = datetime.datetime.today() – datetime.timedelta(days=n)

future_date = datetime.datetime.today() – datetime.timedelta(days=n)

where n represents the number of days in integers

If you wish to get the date for the past 2 weeks, i.e., 14 days, you subtract 14 from the current date.

import datetime
past_date = datetime.datetime.today() - datetime.timedelta(days=14)
print(past_date)

The result is:

2019-10-03 18:38:04.733042

Let's say you want to practice a particular skill for 21 days, to get the future date you add 21 days to the current date as shown below.

import datetime
future_date = datetime.datetime.today() + datetime.timedelta(days=21)
print(future_date)

The result is:

2019-11-07 18:39:11.019086

More Arithmetic Operations With Timedelta

Date and time values can also be compared to determine which is earlier or later. Consider the examples below.

import datetime
now = datetime.time(9, 31, 0)
next_hour = datetime.time(10, 31, 0)
print 'now < next_hour:', now < next_hour

today = datetime.date.today()
next_week = datetime.date.today() + datetime.timedelta(days=7)
print 'today > next_week:', today > next_week

The result is:

now < next_hour: True
today > next_week: False

Time Zones

So far, you have dealt with datetime without any consideration of factors such as timezones or daylight savings. Before you dive in further, let''s get to understand the difference between naive and aware dates. Naive dates and times don''t have any information that can determine things like timezones or daylight savings; They are, however, easier to work with because they are less complicated. Aware dates and times, on the other hand, have enough information to determine their timezones and keep track of daylight savings.

Difference Between DST, GMT, and UTC

GMT is the official timezone used in some countries in Europe and Africa. GMT is shown in 24-hour, 12-hour format, or both. GMT is used to set the local time. For example, in our case above the local time in Berlin is 2019-10-17 09:40:33.614581+02:00 GMT while in Nairobi it is 2019-10-17 10:40:33.592608+03:00 GMT

DST(day light saving )- Countries that have summer change from daylight saving to summer time to make evening daylight to last longer. During DST, these countries turn their clocks forward an hour and revert to standard time during the fall.

UTC (Coordinated Universal Time ) is a time standard for timezones worldwide. UTC is used to keep time synchronized across the world and acts as a reference point for all timezones.

How to Work With Timezones

Let's look at how you write a simple aware datetime

import datetime
dt_now = datetime.datetime.utcnow()
print(dt_now)

The simple program shows a naive datetime object. If you wish to make it an aware datetime, you have to explicitly factor in a timezone. So how can you add information about timezones in our datetime objects? The Python datetime library does not have any module available to work with timezones; you can still use other libraries to add timezone information. One such library is the pytz library.

Suppose you want to get the current time in Nairobi city, you need to use the specific timezone in our program explicitly. To get the timezone in Nairobi, you can use pytz to get all the possible timezones.

import pytz
pytz.all_timezones

Some of the timezones from above are:

['Africa/Abidjan', 'Africa/Accra', 'Africa/Addis_Ababa', 'Africa/Nairobi']

To get the time in Nairobi in timezone will be:

import pytz
import datetime
tz_nairobi = pytz.timezone("Africa/Nairobi")
dt_nairobi =datetime.datetime.now(tz_nairobi)
print(dt_nairobi)

The result is:

2019-10-17 10:40:33.592608+03:00

What about the city of Berlin

import pytz
import datetime
tz_berlin = pytz.timezone("Europe/Berlin")
dt_berlin =datetime.datetime.now(tz_berlin)
print(dt_berlin)

The result is:

2019-10-17 09:40:33.614581+02:00

As you can see, different cities have different timezones even though the dates may be the same.

Converting Timezones

The first thing to keep in mind when making timezone conversions is to ensure all the time attributes you intend to work with are in UTC. Suppose you want to convert the following timezone to America/New_York timezone.

import datetime
import pytz

timezone_berlin = '2018-06-29 17:08:00'
tz_ber_obj = datetime.datetime.strptime(timezone_berlin, '%Y-%m-%d %H:%M:%S')

timezone_newyork = pytz.timezone('America/New_York')
timezone_newyork_obj = timezone_newyork.localize(tz_ber_obj)

print(timezone_newyork_obj)
print(timezone_newyork_obj.tzinfo)

The result is:

2018-06-29 17:08:00-04:00
America/New_York

Other Practical Examples

When storing date, always store them in UTC. See the example below.

import datetime
import pytz
time_now = datetime.datetime.now(pytz.utc)  
print(time_now)

The result for the code above is 2019-10-18 18:41:16.421462+00:00 even though my local time is 2019-10-18 21:41:16.421650+00:00 i.e 9PM. When reading the dates back for display to the user, apply the user''s local timezone using the localize method, as shown below.

import datetime
import pytz
now =datetime. datetime.today())
now_utc = pytz.utc.localize(now)

This now gives me back my local time which is 2019-10-18 21:41:16.421650+00:00

How to Convert Strings Into Datetime

Python strptime() is a method in the datetime module, and its syntax is:

dateobj =datetime.strptime(date_string,format)

date_string, format arguments are strings and mandatory.

Suppose you want to parse the current date and time.

import datetime
current_dt = datetime.datetime.now()
print(current_dt)

The result is:

2019-10-18 20:40:38.115945

The result is in the ISO 8601 format, i.e. (YYYY-MM-DDTHH:MM:SS.mmmmmm), which is the default format. Therefore you can parse any string that is in the same format. The complete list of format derivatives are available on the official strftime website

import datetime
date_string = "10/17/19"
date_obj = datetime.datetime.strptime(date_string, '%m/%d/%y')
print(date_obj)

The result is:

2019-10-17 00:00:00

Examples of String to Datetime Object With strptime

Suppose you have a datetime string represented as "10/17/19 15:02:34", and you would like to convert into a datetime object.

from datetime import datetime
datetime_string = "10/17/19 13:08:45"
datetime_obj = datetime.strptime(datetime_string, '%m/%d/%y %H:%M:%S')
print(datetime_obj)

The result is:

2019-10-17 13:08:45

The format() Function

Dates are written in different formats, for example, the following dates all mean the same things:

Friday, October 17, 2018 10/17/18 10-17-2018

Although they show the same date, the conversion is slightly different. Take a look below.

from datetime import datetime

# Define dates as strings
ds1 = 'Friday, October 17, 2019'
ds2 = '10/17/19'
ds3 = '10-17-2019'

# Define dates as datetime objects
dt1 = datetime.strptime(ds1, '%A, %B %d, %Y')
dt2 = datetime.strptime(ds2, '%m/%d/%y')
dt3 = datetime.strptime(ds3, '%m-%d-%Y')

# Print converted dates
print(dt1)
print(dt2)
print(dt3)

The result is the same for all the conversions

2019-10-17 00:00:00
2019-10-17 00:00:00
2019-10-17 00:00:00

Practical Examples

If the string is in the form of "Oct 17 2019 9:00PM", then you can convert it in this way.

date_string = 'Oct 17 2019 9:00PM'
date_object = datetime.strptime(date_string, '%b %d %Y %I:%M%p')
print(date_object)

The result is:

2019-10-17 21:00:00

You can use strptime() function to convert string to a date object.

from datetime import datetime
date_string = '10-17-2019'

date_object = datetime.strptime(date_string, '%m-%d-%Y').date()
print(type(date_object))
print(date_object)

The result is:

<type 'datetime.date'>
2019-10-17

How to Convert Python Datetime to String

The Pthon datetime module also has the strftime() method that does the opposite (ie. converts datetime and time objects into strings. The syntax for the datetime and time module are:

datetime_string = datetime_object.strftime(format_string)
time_string = datetime_object.strftime(format_string[,time_object])

Examples of Datetime to String With strftime()

Suppose you wish to convert the current datetime into a string?. How do you go about it?. You first get the datetime object representation of the current datetime and call the strftime() method on the object.

import datetime
current_date = datetime.datetime.now()
current_date_string = current_date.strftime('%m/%d/%y %H:%M:%S')
print(current_date_string)

The result is:

10/17/19 16:35:49

How to Obtain the String Representation of Date and Time With the format() Function

Example 1:

In the code below, you''l convert the current timestamp in a datetime object to string in the format "DD-MMM-YYYY (HH:MM:SS:MICROS)"

import datetime
dt_obj =datetime.datetime.now()
dt_string = dt_obj.strftime("%d-%b-%Y (%H:%M:%S.%f)")
print('Current Time : ', dt_string)

The result is:

('Current Time : ', '18-Oct-2019 (11:35:50.665100)')

Example 2: Convert the current timestamp in a datetime object to string in the format HH:MM:SS.MICROS – MMM DD YYYY

import datetime
dt_obj = datetime.datetime.now()
dt_string = dt_obj.strftime("%H:%M:%S.%f - %b %d %Y")
print('Current Time : ', dt_string)

The result is:

('Current Time : ', '11:41:15.575942 - Oct 18 2019')

Other Python Datetime Libraries

Python has other libraries that make manipulation of date-times much easier. Some of them have timezones hence reducing the complexity associated with timezones. Let's look at them below.

Arrow

Arrow is also another powerful python module that makes it easy to create, manipulate, and format dates and times. It is available via pip, and you can install it as follows:

sudo pip3 install arrow

For example, you can use Arrow to get the current time just like the datetime module.

import arrow
current_time = arrow.now()
print(current_time)
print(current_time.to('UTC'))

The result is:

2019-10-17T15:52:58.921198+00:00
2019-10-17T15:52:58.921198+00:00

Maya

Maya makes it very easy to parse strings and convert timezones.

For example

import maya
dt = maya.parse('2018-04-29T17:45:25Z').datetime()
print(dt.date())
print(dt)
print(dt.time())

The result is:

2019-10-17
2019-10-17 17:45:25+00:00
17:45:25

Dateutil

dateutil is a powerful library that can be used to parse dates and times in python in a variety of formats. See the examples below.

from dateutil import parser
dt_obj = parser.parse('Thu Oct 17 17:10:28 2019')
print(dt_obj)
 
dt_obj1=parser.parse('Thursday, 17. October 2019 5:10PM')
print(dt_obj1)
 
dt_obj2=parser.parse('10/17/2019 17:10:28')
print(dt_obj2)
 
t_obj=parser.parse('10/17/2019')
print(t_obj)

The result will be:

2019-10-17 17:10:28
2019-10-17 17:10:00
2019-10-17 17:10:28
2010-10-17 00:00:00

As you can see, you dont need any regular expression to determine the format; the parser looks for recognizable tokens and then guess where it belongs else it throws an error.

Important Points to Keep in Mind

Let's look at some of the best practices to keep in mind when working with Python datetime.

• It is recommended to always work with UTC s this eliminates the need for timezones, which is prone to errors due to time difference in different regions
• When working with dates and times, always use UTC.
• You should only convert datetimes to local time when displaying to the user.

Conclusion

There are many scenarios where you''ll work with date and time in real-world applications. For example:

• When you want to schedule a script to run at some particular timings
• When filtering date from particular days
• When extracting data from certain APIs at specific times every day
• Applications that keep track of events, appointments, or bookings, e.t.c.