42  Exception Handling

Try following code

print(1/0)

You should see following error

Traceback (most recent call last): File “”, line 1, in ZeroDivisionError: division by zero

This example seems meaningless why should we knowingly divide a number by zero. But, consider that we get this values from end user.

a = 1 # from user input
b = 0 # from user input

Or, we need to read a file from system and this filename is again given by user.

filename = "a.txt" # from user input
# try to read content with wrong file name

We will again get an error.

Solution is to surround would be problematic lines with try…except statements See below examples

42.1 Examples

• Exception example: file reading 1
• Exception example: file reading 2
• Exception example: file reading 3

42.2 try..except

42.3 try..except..else

Else part runs if there is no error.

42.4 try..except..else..finally

finally part always runs.

42.5 exception handling hierarchy

• see exception hierarchy in python document
• see following code for generating Python error classes hierarchy
• see this article about this topic too

42.6 Links in our references

• Python 101: Exception Handling

• Non-Programmer’s Tutorial for Python 3/Dealing with the imperfect

42.7 other references

• exceptions in real python
• Python Try Except in w3schools.com

42.8 Video Tutorials