The exception indicates that, although the event can occur, this type of event happens infrequently. When the method is not able to handle the exception, it is thrown to its caller function. Eventually, when an exception is thrown out of the main function, the program is terminated abruptly. In this Python exceptional handling tutorial, you will learn :
What is an Exception in Python? Common Examples of Exception Why should you use Exceptions? Rules of Exceptions Python Exception Handling Mechanism Python Try Statement Python Catch Statement Raise Statement in Python Important Python Errors Other Important Python Exceptions Error vs. Exceptions
Common Examples of Exception:
Division by Zero Accessing a file which does not exist. Addition of two incompatible types Trying to access a nonexistent index of a sequence Removing the table from the disconnected database server. ATM withdrawal of more than the available amount
Why should you use Exceptions?
Here are the reasons for using exceptions in Python:
Exception handling allows you to separate error-handling code from normal code. An exception is a Python object which represents an error. As with code comments, exceptions helps you to remind yourself of what the program expects. It clarifies the code and enhances readability. Allows you to stimulate consequences as the error-handling takes place at one place and in one manner. An exception is a convenient method for handling error messages. In Python, you can raise an exception in the program by using the raise exception method. Raising an exception helps you to break the current code execution and returns the exception back to expection until it is handled. Processing exceptions for components which can’t handle them directly.
Rules of Exceptions
Here are some essential rules of Python exception handling:
Exceptions must be class objects For class exceptions, you can use try statement with an except clause which mentions a particular class. Even if a statement or expression is syntactically correct, it may display an error when an attempt is made to execute it. Errors found during execution are called exceptions, and they are not unconditionally fatal.
Python Exception Handling Mechanism
Exception handling is managed by the following 5 keywords:
try catch finally throw
Python Try Statement
A try statement includes keyword try, followed by a colon (:) and a suite of code in which exceptions may occur. It has one or more clauses. During the execution of the try statement, if no exceptions occurred then, the interpreter ignores the exception handlers for that specific try statement. In case, if any exception occurs in a try suite, the try suite expires and program control transfers to the matching except handler following the try suite.
The catch Statement
Catch blocks take one argument at a time, which is the type of exception that it is likely to catch. These arguments may range from a specific type of exception which can be varied to a catch-all category of exceptions. Rules for catch block:
You can define a catch block by using the keyword catch Catch Exception parameter is always enclosed in parentheses It always represents the type of exception that catch block handles. An exception handling code is written between two {} curly braces. You can place multiple catch block within a single try block. You can use a catch block only after the try block. All the catch block should be ordered from subclass to superclass exception.
Example:
Finally Statement in Python
Finally block always executes irrespective of an exception being thrown or not. The final keyword allows you to create a block of code that follows a try-catch block. Finally, clause is optional. It is intended to define clean-up actions which should be that executed in all conditions. Finally, clause is executed before try statement.
Raise Statement in Python
The raise statement specifies an argument which initializes the exception object. Here, a comma follows the exception name, and argument or tuple of the argument that follows the comma. Syntax: In this syntax, the argument is optional, and at the time of execution, the exception argument value is always none.
Example:
A Python exception can be any value like a string, class, number, or an object. Most of these exceptions which are raised by Python core are classes with an argument which is an instance of the class.
Important Python Errors
Other Important Python Exceptions
Error vs. Exceptions
Summary
An exception is an error which happened during the execution of a program. The exception indicates that, although the event can occur, this type of event happens infrequently. Common Examples of Exception are 1) Division by Zero, 2) Accessing a file which is not existent, 3) Addition of two incompatible types. An exception is a Python object which represents an error. A try statement includes keyword try, followed by a colon (:) and a suite of code in which exceptions may occur. It has one or more clauses. Catch blocks take one argument at a time, which is the type of exception that it is likely to catch. The raise statement specifies an argument which initializes the exception object. Finally, block always executes irrespective of an exception being thrown or not.
