The document explains the concept of exceptions in Python, detailing how they are runtime errors that can be handled by programmers. It outlines the steps for exception handling, including using 'try', 'except', and 'finally' blocks, and provides information on various built-in exception classes. Additionally, it introduces user-defined exceptions and provides guidelines for creating and handling them.

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EXCEPTIONS-PYTHON.pptx RUNTIME ERRORS HANDLING

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  Exceptions
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  DefinitionAn exception isa runtime error which can be handled by theprogrammer. That means if the programmer can guess an error in theprogram and he can do something to eliminate the harm caused bythat error then it is called an exception. If error is not handled byprogrammer then it is called as error.All exceptions are represented as classes in python. The exceptionswhich are already available in python are called built-in exception.
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  Important exception classesin pythonBaseExceptionExceptionStandardError WarningDeprecationWarningRuntimeWarningImportWarningAssertionErrorSyntaxErrorTypeErrorEOFErrorRuntimeErrorImportErrorArthmeticErrorNameError
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  Exception HandlingPurpose ofhandling errors is to make program robust. It means strong.Robust program does not terminate in the middle. When there is a errordisplays appropriate message to the user and continue execution. Whenthe errors can be handled they are called exception.To handle the exception the programmer should perform the followingthree stepsStep1: The statement that may cause the exception must be written insidea ‘try’ blocktry:statementsIf statement raises an error then it enters into except block otherwisecontinues the execution
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  continuedStep2:Programmer should writeexcept block where we should display the exception details to theuserexcept exception name:statements #these statements from handlerStep3:Lastly the programmer should perform clean up actions like closing the files and terminatingany other processes which are running.finally:statementsStatements inside the finally block are executed irrespective of whether there is an exception ornot. This ensures that all the opened files are properly closed and all the running processes areterminated properly.
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  Syntax for handlingexceptiontry:statementsexcept Exception1:exception handler1except Exception2:exception handler2else:statementsfinally:statements
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  Types of ExceptionExceptionClass Name DescriptionException Represents any type of exception. All exception are sub classes of this classArithmeticError Represents the base class for arithmetic errors like OverflowError,ZeroDivisionError, FloatingPointErrorAssertionError Raised when an assert statement gives errorAttributeError Raised when an attribute reference or assignment failsEOFError Raised when input() function reaches end of file condition without reading anydataFloatingPointError Raised when a floating operation failsGeneratorExit Raised when generators close() method is calledIOError Raised when an input or output operation failed. It raises when the file opened isnot found or when writing data disk is fullImportError Raised when an import statement fails to find the module being imported
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  continuedException Class NameDescriptionIndexError Raised when a sequence index or subscript is out of rangeKeyError Raised when a mapping (dictionary) key is not found in the set of existingkeysKeyboardInterrupt Raised when the user hits the interrupt key(Control-C, Delete)NameError Raised when an identifier is not found locally or globallyNotImplementedError Derived from runtimeError
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  Programs on exceptionPythonprogram to handle ZeroDivisionError exceptionFilename:ep1.pyPython program to handle syntax error given by eval() functionFilename:ep2.pyPython program to handle multiple exceptionFilename:ep3.py
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  User Defined ExceptionLikethe built in exceptions of python user can also create his ownexceptions which are called user defined exception or custom exception.EXAMPLE: Matainance of minimum balance in accountSteps to define user defined exception1.Create own exception class and is sub class of built in class Exceptionclass MyExecption(Exception):def __init__(self,arg):self.msg=argmsg is member of class MyException and is assigned with parameterreceived from outside
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  Continued2. When theprogrammer suspects the possibility of exception raise ownexception using raise statementRaise MyExecption(‘message’)3. Programmer must write the code inside a try block and catch theexception using except block astry:codeexcept MyException as meprint(me)Python program to illustrate user defined exceptionFilename:ep4.py
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