How can I achieve user defined exception in Python?

Question

There are many inbuilt exception classes like EOFError, KeyboardInterrupt, etc. But how can I make my own exception class. For instance, if I want to keep constraint that user should enter a string of length minimum three.

Answer 1

Check this code for user-defined exception:

class ShortInputException(Exception):
    def __init__(self,length,atleast):
        Exception.__init__(self)
        self.length = length
        self.atleast = atleast

try:
    text = input('Enter some text: ')
    if len(text) < 3:
        raise ShortInputException(len(text),3)
except EOFError:
    print('It is end of file.')
except ShortInputException as ex:
    print('ShortInputException: You entered {0} length long text. Expected text size is {1}'.format(ex.length,ex.atleast))
except KeyboardInterrupt:
    print('You interrupted the program execution.')
else:
    print('No exception/s raised.')
    print('You entered: {0}'.format(text))

Answer 2

You can define your exception either with in your class or you can create your own exception class in the following .

/** * Define a your exception class which extends Exception */

class Your_Exception extends Exception:

// redefine exception with a message
public function __construct($message, $code = 0, Exception $previous = null):

    //Call Parent constructor
    parent::__construct($message, $code, $previous);


// custom string representation of object
public function __to_String():
    return __CLASS__ . ": [{$this->code}]: {$this->message}\n";


public function user_defined_Function() :
    echo "user defined exception exception\n";