Python raise exception

Python raise exception : Learn how exception raise in python and use of try and except in python programming language. It is used in your program to raise an exception as it breaks the current code execution and returns the exception back until it is handled. To throw or raise an exception we use the raise keyword.

Handling exception:-

The code may raise an exception and you can defend program by placing the code in try: block.
After the try: block an except: statement will follow the code and handle the problem as possible.
Syntax:-
Syntax of the try...except...else block is,
try:
You do operation;
……
except Exception1:
If there is exception1, then execute this block.
except Exception2:
If there is exception2, then execute this block.
…….
else:
no exception exist then then execute this block.
The try statement has multiple except statements and useful when the block contains the statement that throws different types of exception.
Also provide the exception clause and handle any exception.
The except clause can include the else-clause and code is in else block that executes the code in try block and don’t raise an exception.
The else block is good code and do not need the try block protection.
   try:
  print(x)
  except:
  print("An exception occurred")

Raising the exception Example:-

Raise an error and stop program if x is lower than 0:
X=-1
If x<0;
raise Exception (“Sorry, no numbers below zero”)

 

Output:-
Trackback     (most recent call last):
File “demo_ref_raise.py”, line 4, in <module>
Raise Exception (“sorry, no numbers below zero”)
Exception: sorry, no numbers below zero
Use the else keyword to define the block of codes to be executed if no errors are raised:
Example:-
Try block is do not generate the error,
try:
print(“Hello”)
except:
print(“something went wrong”)
else:
print(“Nothing went wrong”)
Output:-
Hello
Nothing went wrong

Example2:-

def enterange (age):
if age<0:
raisevalueError (“Only positive integers are allowed”)
if age %2==0:
print(“age is even”)
else:
print(“age is odd”)
try:
num=int (input (“Enter your age :”))
enterage (num)
except ValueError:
print(“Only positive integers are allowed”)
except:
print(“something is wrong”)
Output:
Enter your age: 12
Age is even again run and enters the negative number
Enter your age:-12
Only integers are allowed
Finally:-
Used to execute if the try block raises an error or not.
Example:-
try:
print(x)
except:
print(“something went wrong”)
finally:
print(“The ‘try except is finished”)
Output:-
Something     went    wrong
The ‘try except’ is finished

Catching the exception in python:-

The exception is handled using the try statement in python language.
But when the exception arises inside try clause the code will handle the exception is written in the except clause.
The try block raises the error and the except block will be executed.
If try block is not used the program will raise an error and get crash.
Example:-
It will raise an error because the x is not defined.
                                 print(x)
Output:-
Trackback (most recent call last):
File “demo_try_except_error.py”, line 3, in<module>
Print(x)
NameError: name’x’ is not defined
Many exceptions:-
The example below will have many exceptions and is described using the example below.
Example:-
try:
print(x)
except NameError:
print("Variable x is not defined")
 except:
 print("Something else went wrong")
Output:-
Variable x is not defined