Python files for understanding exceptional handling

Author: sanjaypradeep

ExceptionalHandling/EHFinally.py

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+
+
+# Important point to be noted.
+
+# finally block is always executed after leaving the try statement. 
+# In case if some exception was not handled by except block, it is re-raised after execution of finally block.
+# finally block is used to deallocate the system resources.
+# One can use finally just after try without using except block, but no exception is handled in that case.
+
+# here's the sample exercise for understanding `finally` keyword in python
+ 
+try: 
+ inFromUser = int(input("Hello user, give me a integer input: "))
+ k = 5//inFromUser # raises divide by zero exception. 
+ print(k) 
+ 
+# handles zerodivision exception 
+except ZeroDivisionError: 
+ print("Can't divide by zero") 
+except TypeError:
+ print("Given in put is not in a right datatype")
+ 
+finally: 
+ # this block is always executed 
+ # regardless of exception generation. 
+ print('This is always executed') 
+
+
+

ExceptionalHandling/ForGoodUnderstanding.py

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+
+'''
+What is Exception?
+
+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. 
+
+'''
+
+# print(1/0) # Syntactically it's right, but do you think this will execute?
+
+# print(name) # have we declared/defined before this line of code?
+
+# What will be the output?
+
+# print('2' + 5) 
+
+
+# To overcome the aboev examples, I'm creating method, which handles the exeptions in it. 
+
+# First example
+
+def division():
+ try:
+ print(1/0)
+ except ZeroDivisionError:
+ print("why are you trying divide a natural number with 0?")
+ except ValueError:
+ print("Value error man..")
+ except TimeoutError:
+ print("time out error sir..")
+
+division()
+
+# Second example
+
+def showName():
+ try:
+ print(name)
+ except ZeroDivisionError:
+ print("why are you trying divide a natural number with 0?")
+ except ValueError:
+ print("Value error man..")
+ except TimeoutError:
+ print("time out error sir..")
+ except NameError:
+ print("You haven't defined any such variable btw")
+ # Stlyish way is..
+ except (RecursionError,NameError,TypeError, ZeroDivisionError):
+ print("I catched.")
+ pass
+
+showName()
+
+# Third Example
+
+def addValues():
+ try:
+ print('2' + 'Sanjay' + 1232)
+ # except TypeError:
+ # print("I don't support this type.")
+ except Exception:
+ print("Master guy says, Something went wrong inside the code.")
+
+addValues()
+
+# Till now, we saw about predefined or system defined exceptions, isn't it?
+# Think about writing our own exceptions?
+
+# JFYI
+
+'''
+When we are developing a large Python program, it is a good practice to place all the user-defined 
+exceptions that our program raises in a separate file. Many standard modules do this. They define their 
+exceptions separately as exceptions.py or errors.py (generally but not always).
+
+
+ser-defined exception class can implement everything a normal class can do, but we generally make them simple and concise. 
+Most implementations declare a custom base class and derive others exception classes from this base class. 
+'''
+
+# first example of user defined exception.
+class SanjayException(Exception): 
+ pass
+
+
+def evenOrOdd(number):
+ if type(number) is not int:
+ raise(SanjayException("input parameter is not in right format"))
+ return True if number %2 ==0 else False
+
+evenOrOdd('Sanjay')
+
+
+# To go even deeper, here's the list of user defined exceptions.
+
+class Error(Exception):
+ """Base class for other exceptions"""
+ pass
+
+
+class ValueTooSmallError(Error):
+ """Raised when the input value is too small"""
+ pass
+
+
+class ValueTooLargeError(Error):
+ """Raised when the input value is too large"""
+ pass
+
+
+# you need to guess this number
+gloal_lucky_number = 10
+
+# user guesses a number until he/she gets it right
+while True:
+ try:
+ userGivenInput = int(input("Enter a number: "))
+ if userGivenInput < gloal_lucky_number:
+ raise ValueTooSmallError
+ elif userGivenInput > gloal_lucky_number:
+ raise ValueTooLargeError
+ break
+ except ValueTooSmallError:
+ print("This value is too small, try again!")
+ print()
+ except ValueTooLargeError:
+ print("This value is too large, try again!")
+ print()
+
+print("Congratulations! You guessed it correctly.")
+
+
+# Q & A ?
+
+
+'''
+Here's the overall predefined exception tree structure.
+
+BaseException
+ +-- SystemExit
+ +-- KeyboardInterrupt
+ +-- GeneratorExit
+ +-- Exception
+ +-- StopIteration
+ +-- StandardError
+ | +-- BufferError
+ | +-- ArithmeticError
+ | | +-- FloatingPointError
+ | | +-- OverflowError
+ | | +-- ZeroDivisionError
+ | +-- AssertionError
+ | +-- AttributeError
+ | +-- EnvironmentError
+ | | +-- IOError
+ | | +-- OSError
+ | | +-- WindowsError (Windows)
+ | | +-- VMSError (VMS)
+ | +-- EOFError
+ | +-- ImportError
+ | +-- LookupError
+ | | +-- IndexError
+ | | +-- KeyError
+ | +-- MemoryError
+ | +-- NameError
+ | | +-- UnboundLocalError
+ | +-- ReferenceError
+ | +-- RuntimeError
+ | | +-- NotImplementedError
+ | +-- SyntaxError
+ | | +-- IndentationError
+ | | +-- TabError
+ | +-- SystemError
+ | +-- TypeError
+ | +-- ValueError
+ | +-- UnicodeError
+ | +-- UnicodeDecodeError
+ | +-- UnicodeEncodeError
+ | +-- UnicodeTranslateError
+ +-- Warning
+ +-- DeprecationWarning
+ +-- PendingDeprecationWarning
+ +-- RuntimeWarning
+ +-- SyntaxWarning
+ +-- UserWarning
+ +-- FutureWarning
+ +-- ImportWarning
+ +-- UnicodeWarning
+ +-- BytesWarning
+'''