Errors:

Unusual and unexpected situations that affect the normal flow of program execution. There are Two types of errors in Python:

• Syntax Error or Compile Time error : These errors occur before the program execution begins, i.e., at the time of compilation.
• Reason for this Error is while writing the code we don’t follow proper rules and structure of the language.
• program will not start executing until we correct all the syntax errors in our code.

	
	def count():
		for letter in 'Sam':
	print(letter)
        
	count()
	

	
	#  Output : 
		File "", line 3
		print(letter)
		^
		IndentationError: expected an indented block
	

• Exception or Run time error: After the code is successfully compiled and execution is in-progress.
• This is due to the errors in our code which occur at run-time and compiler dosen't recognize such errors.
• Python Full list of built-in exception.

	
	ZeroDivisionError: division by zero
		num = 123 / 0
		print(num)	
	
	IndexError: list index out of range
		names=['Aman','Ram','Singh']
		names[3]
	

Exception Handling :

When there is an exception occured in our program, the execution stops and it displays an error message. But if we can handle it, the program will not crash and execution will continue.

• The basic terminology and syntax used to handle errors in Python are the try and except statements. The code which can cause an exception to occur is put in the try block and the handling of the exception is then implemented in the except block of code. The syntax follows:

	
	#  Syntax : 
	try:
	   some operations here...
	   ...
	except ExceptionI:
	   If there is ExceptionI, then execute this block.
	except ExceptionII:
	   If there is ExceptionII, then execute this block.
	   ...
	else:
	   If there is no exception then execute this block.
	

	
	#  Example :
	
	names=['Aman','Ram','Singh']
	try:
		names[3]
	except IndexError as e:
		print(e)
	else:
		print("Name fetched Successfully")
	
	#  Output : 
		list index out of range
	

	
	#  Example : using sys module to print the exception
	
	import sys
	names=['Aman','Ram','Singh']
	try:
		names[3]
	except:
		print(sys.exc_info()
	
	#  Output : 
	(<class 'IndexError'>, IndexError('list index out of range'), <traceback object at 0x000002182A237AC0>)
	

• Else block: else block will get executed - If there is no exception in our code.

	
	#  Example : else block
	
	names=['Aman','Ram','Singh']
	try:
		names[2]
	except IndexError as e:
		print(e)
	else:
		print("Name : {name} fetched successfully.".format(name=names[1]))
	
	#  Output : 
	Name : Ram fetched successfully.
	

• finally: finally block of code will always be executed regardless if there was an exception in the try code block or not.

	
	def inputint():
		while True:
			try:
				val = int(input("Please enter an integer: "))
			except:
				print("The Number you entered was not an Integer !")
				continue
			else:
				print("Great !! That's an Integer")
				print(val)
				break
			finally:
				print("This is finally block executed ")
			
		
	inputint()
	

	
	#  Output : 
		Please enter an Integer : wq
		The Number you entered was not an Integer !
		This is finally block executed
		Please enter an Integer : ?>LK
		The Number you entered was not an Integer !
		This is finally block executed
		Please enter an Integer : 23
		Great !! That's an Integer
		23
		This is finally block executed
	

throwing Exceptions in Python

In python, we can also raise an exception forcefully using raise keyword :

	
	#  raise an OSError : 
	raise OSError
	
	raise OSError('There was an OS Error')
	

Creating our own exception type:

To create our own exception type while create a class we need to inherit Exception class or any other exception class.

To catch this type of exception we can use previous discussed method. (try-except)

	
	class notfellingwell(Exception):
		def __init__(self,temp):
			self.temp = temp
			
		def __str__(self, temp):
			if(self.temp >=38):
				return f'Your body temp is : {self.temp} . Take Rest!!'

	

	
	try:
		raise notfellingwell(40)
	except:
		print("Ignore this temp and enjoy your life!!")