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What is a user defined exception? How is it raised in Python script? |
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Answer» Errors detected during execution are called EXCEPTIONS. In Python, all exceptions must be INSTANCES of a class that derives from BaseException. Python library defines many subclasses of BaseException. They are called built-in exceptions. Examples are TypeError, ValueError etc. When USER code in try: block raises an exception, program control is thrown towards except block of corresponding predefined exception type. However, if the exception is different from built-in ones, user can define a customized exception class. It is called user defined exception. Following example defines MyException as a user defined exception. class MyException(Exception): def __init__(self, num): self.num=num def __str__(self): return "MyException: invalid number"+str(self.num)Built-in exceptions are raised implicitly by the Python interpreter. However, exceptions of user defined type must be raised explicitly by using raise keyword. The try: block accepts a number from user and raises MyException if the number is beyond the range 0-100. The except block then processes the exception object as defined. try: x=int(input('input any number: ')) if x not in range(0,101): raise MyException(x) PRINT ("Number is valid") except MyException as m: print (m)Output: input any number: 55 Number is valid input any number: -10 MyException: invalid number-10 |
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