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