datetime

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Hello folks...!!!

Today let us look at the package datetime and methods available  with it.

General terminologies related to date and time

This module provides various classes to work on the date and time. We use the objects of these classes to perform any kind of action on a date or time. The arithmetic operations cannot be carried out in a normal way on date and time. As we all know, If we add 1 hour to 12.00, then the time should be 1.00 and not 13.00 and adding 1 day to 31st of January should be 1st of February and not 32. To work on such things these classes will be very useful. The basic terminologies one should know before working with this module are listed below.

Time zone

The globe is divided into number of regions. Each region follow a standard time that is convenient for legal and commercial purposes. These regions are referred to as time zones. They are based on the boundaries and not strictly on the longitude.

Time zone offset

Coordinated Universal Time (UTC) is the standard time with which the world's clock and time are regulated. Time zone offset refers to how many hours, the time zone is from the UTC. It is written in the format +/- 00:00. Example: For Asia/Taipei - +08:00 is the offset.

DST

It is expanded as Daylight Saving Time (also Daylight Savings Time). In warmer months, the clocks will be advance one hour from the standard time which makes people feel like the darkness falls later every day according to the clock. This is done in spring season and thus also known as spring forward. When autumn comes, the clocks are set back by one hour and this is called fall back It has a great impact on energy consumption. ON/OFF term is used with the DST while using this module. 

datetime objects

There are two kinds of datetime objects. They are explained below.

      Naive object:

• A naive datetime object does not contain any information regarding the time zone, DST, etc.
• It depends upon the program, whether the shown date and time is a UTC time or corresponds to some other time zone.
• Ambiguity arises when these kind of  objects try to locate itself relative to other datetime objects.

      Aware object

• It has the information on time zones and DST embedded in it.
• It can locate itself relative to other  datetime objects.
• A naive object can be converted into aware object.    

datetime module

The datetime module contains several classes within it. Those classes define variety of functions that helps to manipulate dates and times. To utilize these classes, we have to import them and create an object for it. Using the created object all the functionalities belonging to that class can be accessed. The classes in this module are listed below:

• datetime
• date
• time
• timedelta
• tzinfo
• timezone

We can see the commonly used classes in detail one by one.

datetime.date 

Tip : Instead of writing  datetime.date every time we can write initially as from datetime import date as dt which means from the module datetime import the class date and it is allowed to be called as dt. 

1. date.today( ): 

It returns today's date in the format year-month-date. It can be split into year,month and date components by writing as given in the coding snippet below .

2. date.date( ):

It is used to create a new date object. The parameters required to be passed are year,month and date. This date(y,m,d) is the constructor of the date class in datetime module. For example one can write as dt.date(2019,08,17) which yields 2019-08-17.

3. date.replace():

This is used to replace either the whole date or any component of the date by passing the parameter. Let us consider a list of dates. You are required to change the date 2019-07-23 to 2019-06-23. To do so look at the code below.

    

As we have imported the date class as dt, we call constructor with the name dt while creating the list of dates. The created date objects are appended to the list 'li'. Then the list iterated to find the date to be changed. Once found using the replace method, the month alone is changed here. Some of the other possible replacements in a datetime object are:

• dt.replace(2014,5,2) - changes the whole date. 
• dt.replace(year=2017)- changes the year alone.
• dt.replace(month=6)- changes the month alone.
• dt.replace(day=24)- changes the day alone. 

4. date.timetuple():

It returns a tuple in the time.struct_time format. This struct_time contains the following information about a date object:

• tm_year : four digit year of the datetime object.
• tm_month : month of the datetime object (1 to 12).
• tm_mday : day of the datetime object (1 to 31).
• tm_hour : hours in the datetime object. Here set '0'
• tm_min : minutes in the datetime object. Here set '0'.
• tm_sec : seconds in the datetime object. Here set '0'.
• tm_wday : the week day where '0' indicates Monday. (values : 0 to 6)
• tm_yday : The julian day.
• tm_idst : Is Daylight Saving Time on/off. Values : -1 library determines DST, 0 means OFF, 1 means ON. 

5. date.weekday( ):

It returns a number in range 0 and 6 where 0 indicates monday and so on. We can create a list containing the names of the days and then use this weekday() function's result as index to know the week day of a date. Look at the example given below.

6. date.isoweekday( )

Returns an integer in the range 1 and 7, where 1 indicates monday and so on. 

7. date.isoformat( )

Returns a string which represents the ISO 8601 format ('YYYY-MM-DD').

8. date.__str__( )

A date object is converted to string format using this method. This is equivalent to date.isoformat() .

9. date.strftime( 'formatting string' )

This method is used to format the date object and returns the string format of the date object. There are various directives which can be used for formatting. The directives are nothing but the formatting character we use. For example %y denotes year in two digits while %Y denotes year in four digits. To know more directives check out this link. I have shown some examples below.

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