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A finally block encloses the statements that are always executed whether an exception was thrown by the program or not.






A finally block can be defined at either of two places -



• A finally block can be defined right after the try-except block.
• A finally block can be defined right after the try block(if except block is not defined)

Conditions when a finally block runs :

• If an exception is not thrown out of try block, finally block still runs.



#Python- finally block example 

 
try:
	print("Hello from DecodeJava")
except Exception as e:
	print( "Exception caught : ", e)
finally:
	print("A finally block executes with or without exception") 





Output -




Hello from DecodeJava
A finally block executes with or without exception







If an exception thrown by try block is caught by except block, finally block still runs.




# Python - finally block example

import sys

try:
	i = 'one'
	ab = i + 2
except Exception as e:
	print("Exception caught - ",e)
	print(sys.exc_info())	# This function gives the name of caught exception which was thrown by try block 
finally:
	print("A finally block executes with or without exception")





Output -




Exception caught -  can only concatenate str (not "int") to str
(<class 'TypeError'>, TypeError('can only concatenate str (not "int") to str'), <traceback object at 0x0000000002EF83C8>)
A finally block executes with or without exception



An exception of type TypError is thrown when we try to concatenate a string value with an integer value. An except block is declared with Exception class, which is a superclass of every built-in exception class in Python(except system exiting exception classes). Hence, the except block catches the exception TypeError(a subclass of the Exception class) and finally block runs despite the exception already caught.

Note : A call to function exc_info() of sys module(we have imported this module), has allowed us to gather the exact exception class which was caught in the except block.





If an exception thrown by try block is not caught by except block, the finally block still runs.




# Python - finally block example

import sys


try:
    i
except TypeError as e:
	print("Exception caught - ",e)
finally:
	print("A finally block executes with or without exception")





Output-




A finally block executes with or without exception
Traceback (most recent call last):
  File "C:\Users\RadheKrishna\Desktop\Python Programs\exp9.py", line 7, in <module>
    i
NameError: name 'i' is not defined



In the try block, we have declared a variable named, i, but we have not defined it, leading to a NameError exception, which was not caught by except block because it has declared TypeError exception(a different type of exception than NameError). Despite this, the finally block still runs and an exception is thrown after executing the finally block.




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In the absence of except block, if an exception is thrown by try block, the defined finally block runs.




# Python - finally block example


import sys

try:
    fruits = ["Apple", "Pineapple", "Orange"]	# Defining an array with three elements
    print(fruits[5])	#Accessing an invalid index of array i.e 5
finally:
	print("A finally block executes with or without exception")





Output-




A finally block executes with or without exception
Traceback (most recent call last):
  File "C:/Users/RadheKrishna/Desktop/Python Programs/exp10.py", line 8, in 
    print(fruits[5])
IndexError: list index out of range



Within the try block, we have declared an array with three elements. Next, we have tried to access an array element with an out-of-range index 5, leading to an exception of type IndexError, which is uncaught in the absence of except block. Despite this, the finally block still runs and an exception is thrown after executing the finally block.






In the absence of except block, If an exception is not thrown by try block, the defined finally block runs.




# Python - finally block example


try :
    print("Hello there. Have a happy life! ")
finally:
    print("A finally block executes with or without exception")
    





Output




Hello there. Have a happy life! 
A finally block executes with or without exception

So, a finally block(when defined) always runs, no matter if an exception is thrown or not.

Use of finally block

Objects may hold references to the system resources like memory, files, a database which need to be released in a timely fashion when they are no longer needed. Hence, a finally block usually contains a clean-up code i.e. code to release any of such resources that were referenced or locked in the try block or the code which will not be raising any exception at all.

Example of a finally block

# Python - finally block example


#Declaring a variable named File with None keyword to temporarily not give it a value
file = None


try:
	file = open('D:\File.txt','w');			#creating a file
	file.write('Hello from Python')			#writing data to a file
	file.flush()                                    #flushes the data to a file
		

except Exception as e :
	print("An exception is caught :", e)

finally :
	file.close()		                #cleaning up the resources i.e. closing an opened file.

This program creates a text file named "File" in D drive and writes a string Hello from Python to it. Here we have used finally block to run the clean-up code i.e. by calling the close() function to close the stream after the data is flushed to the file.

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