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Commit e437c96

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Python files for understanding exceptional handling
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‎ExceptionalHandling/EHFinally.py

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# Important point to be noted.
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# finally block is always executed after leaving the try statement.
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# In case if some exception was not handled by except block, it is re-raised after execution of finally block.
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# finally block is used to deallocate the system resources.
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# One can use finally just after try without using except block, but no exception is handled in that case.
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# here's the sample exercise for understanding `finally` keyword in python
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try:
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inFromUser = int(input("Hello user, give me a integer input: "))
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k = 5//inFromUser # raises divide by zero exception.
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print(k)
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# handles zerodivision exception
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except ZeroDivisionError:
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print("Can't divide by zero")
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except TypeError:
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print("Given in put is not in a right datatype")
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finally:
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# this block is always executed
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# regardless of exception generation.
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print('This is always executed')
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'''
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What is Exception?
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Errors detected during execution are called exceptions, if a statement or expression is syntactically correct, it may cause an error when an attempt is made to execute it.
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'''
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# print(1/0) # Syntactically it's right, but do you think this will execute?
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# print(name) # have we declared/defined before this line of code?
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# What will be the output?
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# print('2' + 5)
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# To overcome the aboev examples, I'm creating method, which handles the exeptions in it.
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# First example
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def division():
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try:
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print(1/0)
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except ZeroDivisionError:
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print("why are you trying divide a natural number with 0?")
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except ValueError:
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print("Value error man..")
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except TimeoutError:
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print("time out error sir..")
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division()
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# Second example
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def showName():
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try:
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print(name)
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except ZeroDivisionError:
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print("why are you trying divide a natural number with 0?")
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except ValueError:
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print("Value error man..")
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except TimeoutError:
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print("time out error sir..")
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except NameError:
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print("You haven't defined any such variable btw")
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# Stlyish way is..
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except (RecursionError,NameError,TypeError, ZeroDivisionError):
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print("I catched.")
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pass
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showName()
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# Third Example
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def addValues():
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try:
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print('2' + 'Sanjay' + 1232)
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# except TypeError:
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# print("I don't support this type.")
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except Exception:
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print("Master guy says, Something went wrong inside the code.")
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addValues()
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# Till now, we saw about predefined or system defined exceptions, isn't it?
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# Think about writing our own exceptions?
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# JFYI
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'''
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When we are developing a large Python program, it is a good practice to place all the user-defined
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exceptions that our program raises in a separate file. Many standard modules do this. They define their
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exceptions separately as exceptions.py or errors.py (generally but not always).
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ser-defined exception class can implement everything a normal class can do, but we generally make them simple and concise.
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Most implementations declare a custom base class and derive others exception classes from this base class.
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'''
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# first example of user defined exception.
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class SanjayException(Exception):
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pass
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def evenOrOdd(number):
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if type(number) is not int:
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raise(SanjayException("input parameter is not in right format"))
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return True if number %2 ==0 else False
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evenOrOdd('Sanjay')
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# To go even deeper, here's the list of user defined exceptions.
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class Error(Exception):
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"""Base class for other exceptions"""
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pass
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class ValueTooSmallError(Error):
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"""Raised when the input value is too small"""
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pass
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class ValueTooLargeError(Error):
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"""Raised when the input value is too large"""
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pass
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# you need to guess this number
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gloal_lucky_number = 10
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# user guesses a number until he/she gets it right
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while True:
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try:
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userGivenInput = int(input("Enter a number: "))
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if userGivenInput < gloal_lucky_number:
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raise ValueTooSmallError
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elif userGivenInput > gloal_lucky_number:
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raise ValueTooLargeError
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break
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except ValueTooSmallError:
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print("This value is too small, try again!")
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print()
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except ValueTooLargeError:
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print("This value is too large, try again!")
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print()
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print("Congratulations! You guessed it correctly.")
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# Q & A ?
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'''
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Here's the overall predefined exception tree structure.
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BaseException
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+-- SystemExit
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+-- KeyboardInterrupt
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+-- GeneratorExit
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+-- Exception
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+-- StopIteration
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+-- StandardError
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| +-- BufferError
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| +-- ArithmeticError
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| | +-- FloatingPointError
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| | +-- OverflowError
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| | +-- ZeroDivisionError
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| +-- AssertionError
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| +-- AttributeError
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| +-- EnvironmentError
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| | +-- IOError
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| | +-- OSError
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| | +-- WindowsError (Windows)
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| | +-- VMSError (VMS)
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| +-- EOFError
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| +-- ImportError
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| +-- LookupError
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| | +-- IndexError
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| | +-- KeyError
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| +-- MemoryError
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| +-- NameError
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| | +-- UnboundLocalError
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| +-- ReferenceError
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| +-- RuntimeError
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| | +-- NotImplementedError
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| +-- SyntaxError
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| | +-- IndentationError
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| | +-- TabError
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| +-- SystemError
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| +-- TypeError
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| +-- ValueError
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| +-- UnicodeError
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| +-- UnicodeDecodeError
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| +-- UnicodeEncodeError
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| +-- UnicodeTranslateError
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+-- Warning
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+-- DeprecationWarning
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+-- PendingDeprecationWarning
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+-- RuntimeWarning
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+-- SyntaxWarning
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+-- UserWarning
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+-- FutureWarning
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+-- ImportWarning
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+-- UnicodeWarning
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+-- BytesWarning
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'''

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