Exception Handling
==================
=> In any programming language, there are 2-types of errors we have:
	1) Syntax Errors
	2) Run-time errors
=> The errors which occurs because of invalid syntax or mistake in syntax called as "Syntax errors".
Ex-1:
------
x = 10
if x == 10
	print("Hello")
Output:
-------
SyntaxError: Invalid syntax

Ex-2:
------
print(10 + 20) # 30
print 10 + 20 ==> SyntaxError

Note:
-----
Syntax errors should be responsible by "programmers".
Once all syntax errors are corrected then only the program is going to be considered for the execution.

=> The errors which are occurred during the execution of the program but not because of syntax (here syntax is correct) are called as "Run-time errors"
=> Run-time errors also called as "Exceptions".

Ex-1:
-----
string = "Programming"
print(string[0]) # P
print(string[len(string)]) # IndexError

Ex-2:
-----
print(10/2) # 5.0
print(10/0) # ZeroDivisionError

Ex-3:
-----
a = int(input("Enter value:"))
print(a)

Output:
-------
Enter value: ten
ERROR!
Traceback (most recent call last):
  File "<main.py>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'ten'

What is Exception?
------------------
=> An unwanted and unexpected event that disturbs normal flow of program execution is called as an "Exception".

Ex:
----
a = int(input("Enter value:"))
print(a/0)
print(a)

Output:
-------
Enter value:10
ERROR!
Traceback (most recent call last):
  File "<main.py>", line 2, in <module>
ZeroDivisionError: division by zero

Examples for exceptions in python are:
	ZeroDivisionError
	TypeError
	ValueError
	FileNotFoundError
	IndexError etc.

=> When we want to execute the program normally even an exception occurred then we need to handle exceptions this is the main objective of an exception handling.
=> Exception handling cannot repair the program
this can provide the alternative way to execute the program normally.

Ex:
----
Suppose we want to read a file from virtual computer which is located in "Bangalore".
While executing if the Bangalore file is not available, the program can terminated abnormally.
Instead if we can load the local file then the application can execute normally with alternative way.
 
Default Exception Handling:
----------------------------
=> Every exception in python is an object.
For every exception there is a corresponding class.
=> Whenever an exception occurs, PVM will create the corresponding exception object and will check for handling code. 
If handling code is not available the PVM terminate the program abnormally and prints corresponding exception information to the console.
And the rest of the program won't be executed after the exception statement.

Ex:
----
a = int(input("Enter value:"))
print(a/0)
print(a)

Output:
-------
Enter value:10
ERROR!
Traceback (most recent call last):
  File "<main.py>", line 2, in <module>
ZeroDivisionError: division by zero

Python's Exception Hierarchy:
-----------------------------
BaseException
	Exception
	SystemExit
	GeneratorExit
	KeyboardInterrupt
	
Exception
	AttributeError
	ArithmeticError
	EOFError
	NameError
	LookUpError
	OSError
	TypeError
	ValueError
	

ArithmeticError
	ZeroDivisionError
	FloatingPointError
	OverFlowError

LookUpError
	IndexError
	KeyError

OSError
	FileNotFoundError
	InterruptedError
	PermissionError
	TimeOutError

Customized Exception Handling:
------------------------------
using try-except:
-----------------
code with exception ==> risky code
=> risky code can write in the "try block"
=> Handling code must be write in "except block".

Ex:
----
a = int(input("Enter value:"))
try:
    print(a/0)
except ZeroDivisionError:
    print(a/2)
print(a)

=> when you don't know the type of the exception then also we can handle the exception as like below:

Ex:
----
a = int(input("Enter value:"))
try:
    print(a/0)
except Exception:
    print(a/2)
print(a)

try-except-finally block:
--------------------------
try:
	risky code
except:
	Handling code
finally:
	cleanup code

case-1: When there is no exception
------------------------------------
try:
    print("try")
except Exception:
    print("Except")
finally:
    print("finally")

output:
--------
try
finally

case-2: if there is an exception raised and handled:
----------------------------------------------------
try:
    print("try")
    print(10/0)
except Exception:
    print("Except")
finally:
    print("finally")

Output:
-------
try
Except
finally

case-3: If there is an exception raised but not handled:
---------------------------------------------------------
try:
    print("try")
    print(10/0)
except NameError:
    print("Except")
finally:
    print("finally")

Output:
-------
try
finally
ERROR!
Traceback (most recent call last):
  File "<main.py>", line 3, in <module>
ZeroDivisionError: division by zero

Case-4: With multiple except blocks
------------------------------------
try:
    print("try")
    print(10/0)
except NameError:
    print("Except")
except IndexError:
    print("Index is out of range")
except ZeroDivisionError:
    print("No number is possible to divide with zero")
finally:
    print("finally")