Python Design Patterns – Exception Handling

Handling exceptions is also a primary criterion of design patterns. An exception is an error that happens during the execution of a program. When a particular error occurs, it is important to generate an exception. This helps in curbing program crashes.

Why use exceptions?

Exceptions are convenient ways of handling errors and special conditions in a program. When a user thinks that the specified code can produce an error then it is important to use exception handling.

Example – Division by zero

import sys

randomList = ['a', 0, 2]

for entry in randomList:
   try:
      print("The entry is", entry)
      r = 1/int(entry)
      break
   except:
      print("Oops!",sys.exc_info()[0],"occured.")
      print("Next entry.")
      print()
print("The reciprocal of",entry,"is",r)

Output

The above program generates the following output −

Raising Exceptions

In Python programming specifically, exceptions are raised when corresponding error of code occurs at run time. This can be forcefully raised using the “raise” keyword.

Syntax

>   raise KeyboardInterrupt
Traceback (most recent call last):
...
KeyboardInterrupt