Social Icons

Sunday, August 18, 2019

Python exception: Try - Except

What is an exception

An exception is an operation performed by an interpreter or compiler when an error is detected during the execution of a program. As a general rule, the execution of the program is interrupted, and a more or less explicit error message is displayed.


a = 3
b = 0
print (a / b)
builtins.ZeroDivisionError: division by zero
additional information is displayed, including where the script was found. The error message itself has two parts separated by a double point:
  1. first the type of error that is in case: builtins.ZeroDivisionError 
  2. then a specific information of this error which is in this case: division by zero 
In many cases, it is possible to predict in advance some of the errors that may occur at a particular point in the program, and to include specific instructions at this point, which will be activated only if these errors occur.
In high-level languages ​​such as Python, it is also possible to associate a monitoring mechanism with a whole set of instructions, and thus to simplify the handling of errors that may occur in any of these instructions.

Structure and syntax of an exception

A procedure of this type is usually called an exception handling procedure. Python's uses the statement set:

Exception structure

that allow to catch an error and execute a specific script portion of this error.
It works as follows:
The block of statements that directly follows a try statement is executed by Python if there are no errors. If an error occurs while one of these statements is executing, then Python cancels that offending statement and executes instead the code included in the block following the except statement. If no error has occurred in the statements that follow try, then the block that follows the else statement is executed (if this statement is present).
In any case, program execution may continue with subsequent instructions.
Consider for example of a script that asks the user to type his phone number and that by mistake he types his name! we do not want the program to crash! We only want a warning to be displayed:
"Please enter a number type!"
In this way, we give the user the opportunity to try again to correct their mistake!

Structure and syntax

   [Code that can throw an exception]
except MyException:
  [Code in case of exception]
  [Code in case of no exception]
[code in all cases]

Example of exception handling: intercept a division by zero.

n = int (input ("Type a value of number n: "))
m = int (input ("Type a value of number m: "))
    q = n/m
    print ("The quotient is:" + q)
except ZeroDivisionError:
    print ("No division by zero please")


We can  ignore the ZeroDivisionError instruction and put in place only the except statement:

Example without ZeroDivisionError statement 

n = int (input ("Type a value of number n: "))
m = int (input ("Type a value of number m: "))
    q = n/m
    print ("The quotient is:" + q)
    print ("No division by zero please")

The finally statement

The finally statement is used to execute instructions regardless of the errors generated or not (and even if there is a return). In all cases the instructions placed in finally will be executed.

Example with the finally statement

n = int (input ("Type a value of number n: "))
m = int (input ("Type a value of number m: "))
    q = n/m
    print ("The quotient is:" + q)
except ZeroDivisionError:
    print ("No division by zero please")
    print ("End of the script")

Younes Derfoufi

No comments:

Post a Comment

Learn Python For Beginners

Category Of Mobile Courses

Actualités (644) Adsense (1) Affiliation (1) Algebraic Topology (2) Algorithmic (1) all-news (30) Android (5) Android App (8) Android app without code (4) Android Apps (256) Android Development (4) Android download (2) Android OS (3) AngularJS (1) Automata theory and formal language (5) Bootstrap CSS (1) C programming (5) Category and Functor (8) CMS (3) Computer Glossary (18) Create Mobile App With Ionic Framework (2) CSS (2) CSS-Cascading-Style-Sheets (4) Developpement Java (13) Differential Geometry (1) Django-Python-Framework (15) dropshiping (26) Earn Money by Internet (4) Emplois (23) Framework php (2) Fraud (2) Github (2) HTML (7) IT News (3) Java For Beginners (10) Javascript (12) Kotlin Programming Language (8) Kotlin For Mobile Android (1) Linux Download (2) Marketing (5) Mobile (3) Mobile Courses (4) Mobile Marketing (4) MoneyGram (1) News (721) Node.js (5) Open Source (1) Photoshop (1) Protect Computer (1) Python (36) Python BeautifulSoup (1) Python For Data Science (2) Python PyQt (13) Python Reference (1) Python Source Code (3) Python-Books (6) Python-DVD-Training (1) Python-Exercises (297) Python-Framework (1) Python-IDE (1) Python-Kivy-Framework (2) Python-Modules (1) Python-pdf (2) Python-pyQt (1) python-temp (3) Référencement (2) Script PHP (2) Security (6) SEO (1) Snipping Tool: Faq (1) Social Networks (1) Source Code (4) Statistics With SPSS (2) Surveillance Software (1) Travail à domicile (6) Tutoriels php en vidéos (2) Tutoriels-MySql (6) tutoriels-php (19) Utilitaires (1) VPS (1) Web Hosting (1) Webcam (1) Webmarketing (11) Western Union (1) Windows 10 (1) Windows 7 (4) Windows 7 Faq (2) Windows 8 (1) Windows Accessories (1) Windows Download (8) Windows Drivers (1) Windows Fonts (1) Windows Power Shell (2) Windows Registry (2) Windows Security (18) Windows Software (2) Windows Spyware (2) Windows utilities (3) Windows Virus (2) Windows Vista (3) Windows Wireless (1) Windows xp (1) Wordpress (1)

Sample text

Sample Text

Blogger Templates