Exception Handling In Python | Exceptions In Python | Python Programming Tutorial | Edureka

Python Certification Training www.edureka.co/python

Python Certification Training www.edureka.co/python Agenda Exception Handling In Python

Python Certification Training www.edureka.co/python Agenda Introduction 01 Why need Exception Handling? Getting Started 02 Concepts 03 Practical Approach 04 What are exceptions? Looking at code to understand theory Process of Exception Handling

Python Certification Training www.edureka.co/python Why Need Exception Handling? Exception Handling In Python

Python Certification Training www.edureka.co/python Why Need Exception Handling? Dividing by zero Kid Programmer

Python Certification Training www.edureka.co/python Why Need Exception Handling? Dividing by zero Beautiful Error Message! Traceback (most recent call last): File, line 1, in <module> ZeroDivisionError: integer division or modulo by zero

Python Certification Training www.edureka.co/python What Is Exception Handling? Exception Handling In Python

Python Certification Training www.edureka.co/python What Is Exception Handling? An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program's instructions Definition of Exception Process of responding to the occurrence, during computation, of exceptional conditions requiring special processing – often changing the normal flow of program execution Exception Handling What is an exception? What is exception handling? Let us begin!

Python Certification Training www.edureka.co/python Process of Exception Handling Exception Handling In Python

Python Certification Training www.edureka.co/python Process of Exception Handling Everything is fixable!How? Handle the Exception User Finds Anomaly Python Finds Anomaly User Made Mistake Fixable? Yes No Find Error Take Caution Fix Error “Catch” “Try” If you can’t, Python will! I love Python!

Python Certification Training www.edureka.co/python Process of Exception Handling Important Terms Keyword used to keep the code segment under checktry Segment to handle the exception after catching itexcept Run this when no exceptions existelse No matter what run this code if/if not for exceptionfinally

Python Certification Training www.edureka.co/python Process of Exception Handling Visually it looks like this!

Python Certification Training www.edureka.co/python Coding In Python Exception Handling In Python

Python Certification Training www.edureka.co/python Coding In Python Python code for Exception Handling >>> print( 0 / 0 )) File "<stdin>", line 1 print( 0 / 0 )) ^ SyntaxError: invalid syntax Syntax Error >>> print( 0 / 0) Traceback (most recent call last): File "<stdin>", line 1, in <module> ZeroDivisionError: integer division or modulo by zero Exception

Python Certification Training www.edureka.co/python Raising An Exception We can use raise to throw an exception if a condition occurs x = 10 if x > 5: raise Exception('x should not exceed 5. The value of x was: {}'.format(x)) Traceback (most recent call last): File "<input>", line 4, in <module> Exception: x should not exceed 5. The value of x was: 10

Python Certification Training www.edureka.co/python AssertionError Exception Instead of waiting for a program to crash midway, you can also start by making an assertion in Python import sys assert ('linux' in sys.platform), "This code runs on Linux only." Traceback (most recent call last): File "<input>", line 2, in <module> AssertionError: This code runs on Linux only.

Python Certification Training www.edureka.co/python Try and Except Block Exception Handling In Python

Python Certification Training www.edureka.co/python Try And Except Block The try and except block in Python is used to catch and handle exceptions def linux_interaction(): assert ('linux' in sys.platform), "Function can only run on Linux systems." print('Doing something.') try: linux_interaction() except: pass Try it out!

Python Certification Training www.edureka.co/python Try And Except Block The program did not crash! try: linux_interaction() except: print('Linux function was not executed') Linux function was not executed

Python Certification Training www.edureka.co/python Function can only run on Linux systems. The linux_interaction() function was not executed Try And Except Block Example where you capture the AssertionError and output message try: linux_interaction() except AssertionError as error: print(error) print('The linux_interaction() function was not executed')

Python Certification Training www.edureka.co/python Could not open file.log Try And Except Block Another example where you open a file and use a built-in exception try: with open('file.log') as file: read_data = file.read() except: print('Could not open file.log') If file.log does not exist, this block of code will output the following:

Python Certification Training www.edureka.co/python Exception FileNotFoundError Raised when a file or directory is requested but doesn’t exist. Corresponds to errno ENOENT. Try And Except Block In the Python docs, you can see that there are a lot of built-in exceptions that you can use try: with open('file.log') as file: read_data = file.read() except FileNotFoundError as fnf_error: print(fnf_error) [Errno 2] No such file or directory: 'file.log' If file.log does not exist, this block of code will output the following:

Python Certification Training www.edureka.co/python Try And Except Block Another Example Case try: linux_interaction() with open('file.log') as file: read_data = file.read() except FileNotFoundError as fnf_error: print(fnf_error) except AssertionError as error: print(error) print('Linux linux_interaction() function was not executed') If the file does not exist, running this code on a Windows machine will output the following: Function can only run on Linux systems. Linux linux_interaction() function was not executed [Errno 2] No such file or directory: 'file.log'

Python Certification Training www.edureka.co/python Try And Except Block Key Takeaways • A try clause is executed up until the point where the first exception is encountered. • Inside the except clause, or the exception handler, you determine how the program responds to the exception. • You can anticipate multiple exceptions and differentiate how the program should respond to them. • Avoid using bare except clauses.

Python Certification Training www.edureka.co/python The else Clause Exception Handling In Python

Python Certification Training www.edureka.co/python The else Clause Using the else statement, you can instruct a program to execute a certain block of code only in the absence of exceptions

Python Certification Training www.edureka.co/python The else Clause Example Case try: linux_interaction() except AssertionError as error: print(error) else: print('Executing the else clause.') Doing something. Executing the else clause.

Python Certification Training www.edureka.co/python The else Clause You can also try to run code inside the else clause and catch possible exceptions there as well: try: linux_interaction() except AssertionError as error: print(error) else: try: with open('file.log') as file: read_data = file.read() except FileNotFoundError as fnf_error: print(fnf_error) Doing something. [Errno 2] No such file or directory: 'file.log'

Python Certification Training www.edureka.co/python The finally Clause Exception Handling In Python

Python Certification Training www.edureka.co/python The finally Clause finally is used for cleaning up!

Python Certification Training www.edureka.co/python The finally Clause finally is used for cleaning up! try: linux_interaction() except AssertionError as error: print(error) else: try: with open('file.log') as file: read_data = file.read() except FileNotFoundError as fnf_error: print(fnf_error) finally: print('Cleaning up, irrespective of any exceptions.') Function can only run on Linux systems. Cleaning up, irrespective of any exceptions.

Python Certification Training www.edureka.co/python Summary Exception Handling In Python

Python Certification Training www.edureka.co/python Summary In this session, we covered the following topics: • raise allows you to throw an exception at any time. • assert enables you to verify if a certain condition is met and throw an exception if it isn’t. • In the try clause, all statements are executed until an exception is encountered. • except is used to catch and handle the exception(s) that are encountered in the try clause. • else lets you code sections that should run only when no exceptions are encountered in the try clause. • finally enables you to execute sections of code that should always run, with or without any previously encountered exceptions.

Python Certification Training www.edureka.co/python Summary Python Programming, yay!

Exception Handling In Python | Exceptions In Python | Python Programming Tutorial | Edureka

Exception Handling In Python | Exceptions In Python | Python Programming Tutorial | Edureka

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Exception Handling In Python | Exceptions In Python | Python Programming Tutorial | Edureka