Introduction to Exception Handling

Being a programmer everybody encounters errors. These can be very frustrating and make coding feel like a hopeless one. However understanding the errors and exceptions in a program it becomes easier to fix them.

Error and Exception

An Error “indicates serious problems that a reasonable application should not try to catch.” An Exception “indicates conditions that a reasonable application might want to catch.” Error along with RuntimeException & their subclasses are unchecked exceptions. All other Exception classes are checked exceptions.

Exception

An exception can be defined by the following ways:

• An exception is an object in Python. It provides us information regarding an error which is found when you execute a program.
• An exception is also said as an event that occurs during program execution and interrupts the flow of execution.

When a python program raises an exception, it must be handled immediately.

Why use Exceptions?

Exceptions are convenient in many ways of handling errors and special conditions in a program. If you have a code which can produce an error then you can use exception handling.

Differences between Error and Exception:

Exception handling

The process of handling exceptions (that interrupts the normal execution flow of a program) during program execution like number divided by zero, accessing array out of bound and so on is known as “Exception Handling”.

Standard exceptions

Python provides the following exceptions:

1. SyntaxError
2. ZeroDivisionError
3. NameError
4. ValueError
5. TypeError
6. IndexError
7. AttributeError
8. AssertionError
9. ImportError etc

(We will discuss the above exceptions in further section briefly).

Raising an Exception

By using raise exception statement you can raise an exception in your own code. Whenever we raise an exception it breaks current code execution and returns the exception back until it is handled.

Ex 1:The below is an example of raising an exception.

>>> def ValueError(Exception):
	pass

>>> raise ValueError
Traceback (most recent call last):
  File "<pyshell#3>", line 1, in <module>
    raise ValueError
ValueError

Ex 2: Another way to raise an exception by using only a raise statement is as follows:

User-Defined exceptions

In python we are allowed to create our own exceptions with the help of standard built-in exceptions.

We can observe this with the following example. Here the example relates to RunTimeError.

Output

Argument of an Exception:

An exception can have an argument, which is a value that provides extra information regarding problem. The contents of the argument vary by exception. You capture an exception’s argument by supplying a variable in the except clause as follows:

Syntax:

 Ex: The following is an example program of an argument of an exception.

x=26
def temp_convert(var):
    try:
        return int(var)
        print(int(var))
    except ValueError as x:
            print("it should accept only integers",x)
print(x)
temp_convert(26)

Output

The assert statement:

When it identifies an assert statement, Python evaluates the accompanying expression, which is hopefully true. If the expression is false, Python raises anAssertionError exception.

Syntax:

Ex:

Output

0

0