Logging the Exceptions

It is highly recommended to store the complete application flow and exception information in a file.

This process is called Logging.

The main advantages of Logging are:

1. We can use log files while performing debugging.
2. We can provide statistics such as the number of requests per day.

To implement Logging, Python provides one inbuilt module.

This module is used to create log files and write log messages.

Depending on the type of information, logging data is divided into the following 6 levels.

By default, while executing a Python program, only WARNING level and higher level messages will be displayed.

That means, by default, messages of the following levels are shown:

• WARNING
• ERROR
• CRITICAL

Messages of these levels are not displayed by default:

• DEBUG
• INFO

To perform Logging:

1. Create a file to store log messages.
2. Specify which level of messages should be stored.

We can do this by using the basicConfig() function of the logging module.

logging.basicConfig(filename='log.txt', level=logging.WARNING)

Explanation:

• filename='log.txt'
  • Creates a log file named log.txt.
• level=logging.WARNING
  • Stores WARNING level messages and all higher level messages.

The following statement:

After creating the log file, we can write messages by using the following methods.

Import logging module
        │
        ▼
Configure Logging
(using basicConfig)
        │
        ▼
Create Log File
        │
        ▼
Write Log Messages
(debug/info/warning/error/critical)

This flow summarizes the Logging process described in the PDF.

1. Logging is used to store application flow and exception information in a file.
2. Log files are useful while debugging applications.
3. Python provides the built-in logging module for implementing Logging.
4. Logging information is divided into six levels.
5. By default, only WARNING and higher-level messages are displayed.
6. basicConfig() is used to configure the log file and logging level.
7. filename specifies the name of the log file.
8. level specifies which messages should be stored.
9. After configuring logging, messages can be written using the five logging methods provided in the PDF.

Question:

Write a Python program to create a log file and write WARNING and higher level messages.

After executing the above program, the log.txt file contains:

Step 1

Configure Logging.

This creates the log.txt file and stores WARNING level and higher-level messages.

Display a normal message on the console.

This message is printed on the console only.

It is not written to the log file.

Write log messages.

Reason:

The logging level is set to WARNING.

In the above program, only WARNING level and higher-level messages will be written to the log file.

If we set the logging level to DEBUG, then all messages will be written to the log file.

Since the logging level is DEBUG, every logging message is written into the file.

That includes:

• DEBUG
• INFO
• WARNING
• ERROR
• CRITICAL

We can format log messages to include:

• Date
• Time
• IP address of the client
• Other information

This is done at the advanced level.

1. logging.basicConfig() is used to configure the logging system.
2. When the logging level is WARNING, only WARNING and higher-level messages are stored.
3. DEBUG and INFO messages are ignored when the level is WARNING.
4. When the logging level is DEBUG, all logging messages are stored.
5. The print() function displays messages on the console and does not write them to the log file.
6. Log messages can be formatted to include additional information such as date, time, and client IP address at the advanced level.

By using the following function, we can write exception information to the log file.

Question:

Write a Python program to write exception information to the log file.

Input

Execution Flow

Request Started
      │
      ▼
Read First Number
      │
      ▼
Read Second Number
      │
      ▼
Division Successful
      │
      ▼
Request Processing Completed

Since there is no exception, the division is performed successfully.

Input

When the second number is 0, Python raises a ZeroDivisionError.

The program:

• Prints:

cannot divide with zero

• Writes complete exception information to mylog.txt by using:

Input

The input "ten" cannot be converted into an integer.

Python raises a ValueError.

The program:

• Prints:

Enter only int values

• Stores complete exception information in mylog.txt by using:

The program stores logging information in the following file:

mylog.txt

The log file contains:

• Information messages.
• Exception details whenever an exception occurs.

Writes a message when a new request starts.

This function writes exception information into the log file whenever an exception occurs.

Start Program
      │
      ▼
Configure Logging
      │
      ▼
Write "A New request Came:"
      │
      ▼
Read First Number
      │
      ▼
Read Second Number
      │
      ▼
Perform Division
      │
      ├───────────────────────┐
      │                       │
      ▼                       ▼
 Success             Exception Occurs
      │                       │
      │              ├──► ZeroDivisionError
      │              │          │
      │              │          ▼
      │              │ logging.exception(msg)
      │              │
      │              └──► ValueError
      │                         │
      │                         ▼
      │                logging.exception(msg)
      │
      ▼
Write "Request Processing Completed"
      │
      ▼
End

1. Exception information can be written to a log file by using logging.exception(msg).
2. In this program, the log file name is mylog.txt.
3. logging.info("A New request Came:") writes a message when a new request starts.
4. logging.info("Request Processing Completed") writes a message after request processing is completed.
5. If a ZeroDivisionError occurs, the exception information is written to the log file.
6. If a ValueError occurs, the exception information is written to the log file.
7. logging.exception() is used inside the except blocks to record exception details.