![raise statement
It is used to throw an exception. The syntax is as follows:
raise exception-name[(optional argument)]
Note: The optional argument is a string passed to the
exception, that displays the message.
Example:](https://image.slidesharecdn.com/exceptionhandling-241112043230-1b01df17/85/Exception-handling-with-python-class-12-pptx-9-320.jpg)
Exception handling with python class 12.pptx
- 2. Exception Handling As a student of computer science, you know that many times while executing the program we are getting some errors. Errors are problems in a program due to which will stop the program from execution. These errors are categorized as follows:
- 3. Syntax Errors : occures when the program is not written correctly as per the format required Example : x =+ 2 Semantic Errors : occur when the statement has no meaning in the program. Example: a=5 #Sattement 1 b=7 #Statement 2 a+b=res #Statement 3
- 4. Exceptions An exception is a program event that occurs during program execution and disrupts the flow of a program. When a python program cannot Handle with a situation, it raises an exception. An exception is a Python object that represents an error. Some common Python Build-in exceptions are as follows: 1) SyntaxError: This exception is raised when the interpreter encounters a syntax error the code, such as a misspelled keyword, a missing colon, or an unbalanced parenthesis. 2) TypeError: This exception is raised when an operation or function is applied to an object of the wrong type, such as adding a string to an integer.
- 5. 3) NameError: This exception is raised when a variable or function name is not found in the current scope. 4) IndexError: This exception is raised when an index is out of range for a list, tuple, or other sequence types. 5) KeyError: This exception is raised when a key is not found in a dictionary. 6) ValueError: This exception is raised when a function or method is called with an invalid argument or input, such as trying to convert a string to an integer when the string does not represent a valid integer. 7) AttributeError: This exception is raised when an attribute or method is not found on an object, such as trying to access a non- existent attribute of a class instance.
- 6. 8) IOError: This exception is raised when an I/O operation, such as reading or writing a file, fails due to an input/output error. 9) ZeroDivisionError: This exception is raised when an attempt is made to divide a number by zero. 10) ImportError: This exception is raised when an import statement fails to find or load a module.
- 7. Raising Exceptions Exceptions are raised when the program is syntactically correct, but the code results in an error. This error does not stop the execution of the program, however, it changes the normal flow of the program. Example: a = 10 / 0 print(a)
- 8. User-defined exceptions The exception created by the programmer according to the requirement of the program is called user-defined exceptions. The user defined-exception can be created using two methods: 1) raise statement 2) assert statement
- 9. raise statement It is used to throw an exception. The syntax is as follows: raise exception-name[(optional argument)] Note: The optional argument is a string passed to the exception, that displays the message. Example:
- 10. assert statement An assert statement is used to check a condition in the program code. If the result after evaluation is false, then the exception is raised. The syntax for the assert statement is: If this expression is false, an AssertionError exception is raised which can be handled like any other exception. Example:
- 11. What is Exception Handling in Python The process of catching and preventing errors when they occurred is called exception handling. It is a mechanism to overrule the exceptions using some blocks. It is the concept of error handling when something goes wrong, tracking the error, and calling the handling code. The following terms are used for exception handling:
- 12. handling exceptionsusing try-except-finally blocks try: # Some Code....which may have runtime error except: # optional block # Handling of exception (if required) else: # execute if no exception finally: # Some code .....(always executed)
- 13. try: k = 9//0 # raises divide by zero exception. print(k) # handles zerodivision exception except ZeroDivisionError: print("Can't divide by zero") finally: # this block is always executed # regardless of exception generation. print('This is always executed')
- 14. Lets see some example’s for better understanding of Try and Except block
- 15. Use of try and except
- 18. Process of Handling Exception Step 1: The exception object is created by a Python interpreter that contains information related to the error such as type, file name, and position where an error has occurred. Step 2: The object is handed over to the runtime system to find an appropriate code to handle exceptions. This process is called throwing an exception. Step 3: The runtime system searches for a block of code known as an exception handler that handles the raised error. First, it searches for the method by which the error has occurred. If not found then it search method from which this method is called. This process continues till the exception handler is found. When it found a handler it will be executed. This process is known as catching. Step 4: Finally the program gets terminated
- 19. Advantages of Exception Handling: • Improved program reliability • Simplified error handling • Cleaner code • Easier debugging Disadvantages of Exception Handling: • Performance overhead • Increased code complexity • Possible security risks
- 20. Thank You Any doubts ?
- 21. Assignment Questions Q.1 What is exception handling explain with example. Q.2 What are the advantages and Disadvantages of Exception handling. Q.3 Explain the use of try-except-else-finally blocks. Q.4 Write a short note on assert and raise statment Q.5 Explain the process of Handling Exception.