Chapter 9 : Other Important Topics

9.1: range ( ) function

Python range( ) function returns a sequence of integer numbers. In order to traverse through the number we need for loop.

The syntax is:

range ( start, stop )

or

range ( start, stop , step)

Please note: The default value of start is 0.

Example:

Code explanation:

Output

9.2: How to get date, time and time zone in Python

In order to work with date and time Python provides us with datetime and time modules.

But among the two modules, I prefer using time module because we can not only get the date and time but we can also access other information like time zone.

Example:

Code explanation:

In the above piece of code, we get the current local time using localtime( ) function and then format the time using strftime( ) function

What is localtime( ) function in Python?

The localtime( ) function is used to convert a time ( in seconds ) since the epoch to a struct_time.

The syntax is:

time.localtime( t ) , where t is the time in seconds.

If t is not provided, then the localtime( ) function returns the current date and time.

What is epoch in Python?

In Python, time is measured from 1 st Jan 12.00 AM, 1970 and this very time is termed as epoch .

What is struct_time ?

struct_time is a tuple containing 8 elements and they can be accessed by their index value and attribute names.

The elements are as follows:

Index	Attribute	Value
0	tm_year	Year – Example 2020
1	tm_mon	Month- from 1 to 12
2	tm_mday	Day of month – from 1 to 31
3	tm_hour	Hour – from 0 - 23
4	tm_min	Minutes – from 0 to 59
5	tm_sec	Seconds – from 0 to 59
6	tm_wday	Day of the week – from 0 to 6 – Monday 0, Tuesday 1 and so on
7	tm_yday	Day of the year – from 1 to 366
8	tm_isdst	daylight saving flag (0, 1 or -1). A value of 1 indicates that the daylight savings is in effect, 0 if daylight savings is not in effect and -1 if the information is not available.

Along with these 8 elements, there is a newly added attribute named tm_zone .

What is strftime( ) in Python?

strftime( ) is used to convert a struct_time to a string as specified by the format argument .

The syntax is:

time.strftime(“ format_code ”, t), w here t is the time to be formatted.

Commonly used format codes are:

Format Code	Value
%A	returns weekday. Example: Monday
%d	returns day of the month in number. From 0 to 31
%B	returns month. Example: December
%m	returns month in number. Example: from 0 to 12
%Y	returns year. Example: 2020
%H	returns hours from 00 - 23. Example: from 00 to 23
%M	returns minutes from 00-59. Example:30
%S	returns seconds from 00-59. Example: 20
%T	returns current time, equal to %H:%M:%S
%Z	returns timezone.

Now let's run the above piece of code,

The date, time and timezone shows perfectly.

9.3: Python Logging

• Logging helps to understand the basic flow of the program and it is crucial for debugging any issue.

It is very important to add logs at places that will aid with understanding the program flow and the point of failure in various environments (as in dev, staging, prod, etc)

• In order to work with Python logging, we need to import the logging module first. Logging module provides methods to log events according to their level of severity. The levels are:

DEBUG

INFO

WARNING

ERROR

CRITICAL

By default, Python skips logging information from severity level DEBUG and INFO and prints only from severity level WARNING and above.

In order to make Python print all the log messages from all severity level, we need to configure the logging by using basicConfig( ) method .

Some of the commonly used parameters for  basicConfig( )  method are as follows:

1. level : This specifies the root severity level from which the log messages will start displaying.

2. filename : This specifies the log file.

3. filemode : This specifies the mode in which the log file will open. w means write mode The default is  a , which means append .

4. format : This specifies the format of the log message which will appear on the log file.

You can find all the format symbols in Python documentation https://docs.python.org/3/library/logging.html

Example:

Code explanation:

• In the above piece of code, we configured the logging from Line 2 – 5 .

• We set the level to DEBUG , this means that the logging information will get displayed from severity level DEBUG and higher.

• We set the filename. All logging information will get displayed in a log file (logFile.log).

• We set the filemode to w . This specifies that every time the Python module runs, the log file gets overwritten.

• We set the format .

Now let’s run the above piece of code.

The log file generated successfully.

9.4: What does the line if__name__ == __main__ mean in Python?

if __name__ == “__main__” , mean that if a Python file is running directly as the main python file and not imported then set the value of python special variable __name__ equal to __main__   .

main( ) function is executed when the class is executed as an independent unit.

Let us consider the example below,

• Create a new Python file and name it numbers.py

Code explanation:

• We created a class Numbers which has two attributes num1 , num2 and a function add( ).

(To understand Python class, please refer to Chapter 9 )

• if __name__ == “__main__”   meaning that if the file is running directly, then create an object n of class Numbers , pass the arguments and call the function add( ).

• if __name__ is not equal to __main__” meaning that if the file is not running directly then print “ Numbers module is imported ”

Now let’s run the above piece of code

• Now let’s create another Python file letters.py

In this file, we imported the numbers module created above.

Now let’s run the letters.py file.

After running the letters.py , we got three outputs:

Output 1: The first output is generated from the numbers module. Since numbers module is running from letters module and not running directly, then the variable __name__ of numbers module is not equal to “__main__”, hence we get the output “ Numbers module is imported ” . (Please refer to code present in numbers.py)

Output 2: The second output is generated from letters module. Since the letters module is running directly as the main python file so the variable __name__ of letters module becomes equal to “__main__”, hence we get the output “ Letters module is not imported ”