try except and finally

Exception handling in Python with try, except, and finally keywords.


The try, except, and finally are the keywords in Python for exception handling. An exception is a runtime error, that causes the program to stop.

Why we need exception handling? Exceptions are not the errors introduced intentionally, neither they are validation checks. An exception occurs if a program can not process the given data values.

For example, while writing a division function in a server program you forgot to put a validation of zero value for the divisor.

All works well until the divisor is non-zero. What if it is zero? If the program does not hadle this exception, the program will crash and the server needs to start again. Not a good practice at all.

With exception handling, server program will not stop and a user can print a message and read next request.

What try, except, and finally keywords do?

These are the keywords in python for exception handling. Each keyword has its own associated block of code. A try block contains the actual programmer’s code. The execution reaches the except where there is an exception in the try block and the code within finally block always executes.

try:
     #User application code
 except Exception:
     #Executes upon exception
 finally:
     #Always executes

Python code example – No exception – Division by zero

try:
     x = 6;
     print(x/2);    
 except Exception:
     print("Exception while division");
 finally:
      print("Execution Completed");

Output->

3.0
 Execution Completed

Python code example – With exception

try:
     x = 6;
     print(x/0);    
 except Exception:
     print("Exception while division");
 finally:
      print("Execution Completed");
   

Output->

Exception while division
 Execution Completed

Print The exception – Know what exactly error where there could be multiple exceptions-

try:
     x = 6;
     print(x/0);    
 except Exception as e:
     print('Exception :', e);    
 finally:
      print("Execution Completed");

Output->

Exception : division by zero
 Execution Completed