Python Exceptions Powerpoint Presentation

Python Exceptions Powerpoint Presentation

• 1.
  EXCEPTION HANDLING IN PYTHON By:-Animesh Naugai
• 2.
  So…. what isEXCEPTION HANDLING ?  Exception Handling is the process of handling the expected or unexpected exceptions.  You can even raise a user defined error message.  There are several Exception Handling specific keywords in python.  For Exception Handling you don’t need to import any internal or external library or module.
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  Using Exception Handlingwe can avoid unexpected termination during code execution process and most importantly avoiding those scary looking error messages. For example :-  below there are two image of same error(ZeroDivisionError, which happens when we try to perform division by zero) (a) is with out exception handling whereas (b) is with exception handling.  We can see the difference between two (b) much more friendly whereas (a) is nerdy. Why do we need Exception Handling ? (a (b
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  What is anException ?  Exceptions are a means of breaking out of the normal flow of control of a code block in order to handle errors or other exceptional Conditions.  An exception is *raised* at the point where the error is detected; it may be *handled* by the surrounding code block or by any code block that directly or indirectly invoked the code block where the error occurred.
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  The hierarchical representationof EXCEPTIONS is below :- **Note** Whenever an exception is caught by the handler it will return exception class instance according to the **except** clause. Which means other than just the exception class name it will also contain the stack traceback, except when the exception is "SystemExit".
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  How do wehandle exceptions ? In python we some special keywords to implement the exception handling, which are as follows :-  Try : *try* statement is the start of exception handling block.  Except : *except* statement is the end of exception handling block.  Raise : *raise* statement allows user to raise exception.  Finally : *finally* statement is used as clean up section for safe termination. Lets look at each of them with some code………….
• 7.
  Basic exception handlingcode looks like this .. Now if we try to run it, it will ask us to enter a number but u can enter an alphabet too in which case it will cause the error while converting alpha character to integer which will look like this .. So what actually happened here is that it asked a number and we entered non numeric value to it which caused a runtime error or an exception.
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  In previous exampleit was pretty obvious about the type of error but what happen if there are multiple statements inside ‘try – except’ block. Now if we run it again we will need to enter a value and If we enter an non-numeric value result will be “ValueError” whereas on entering a numeric value doesn’t give anything except if we enter ‘0’ which will return “DivisionByZeroError” just as shown in the image. **Note** Some() function is same as code above.
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  There is aadd on to this try-except block which is capability of using else and finally keywords. Finally keyword is used as cleanup section it runs regardless of whether ‘try-except’ block has caught any error or not, except when any syntax error or forced termination occurs. Here is how it looks like in code ..
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  The else statementexecutes if no exception has been caught by ‘try-except’ block. The use of the else statement with ‘try-except’ block is better than adding additional code to the try clause because it avoids accidentally catching an exception that wasn’t raised by the code being protected by the ‘try-except’ block. In the right most image we some stack traceback report telling error with line number, here during handling of ‘ValueError’ another error occurred which wasn’t handled by ‘try-except’.