EXCEPTIONS-PYTHON.pptx RUNTIME ERRORS HANDLING
- 1. Exceptions
- 2. Definition An exception is a runtime error which can be handled by the programmer. That means if the programmer can guess an error in the program and he can do something to eliminate the harm caused by that error then it is called an exception. If error is not handled by programmer then it is called as error. All exceptions are represented as classes in python. The exceptions which are already available in python are called built-in exception.
- 3. Important exception classes in python BaseException Exception StandardError Warning DeprecationWarning RuntimeWarning ImportWarning AssertionError SyntaxError TypeError EOFError RuntimeError ImportError ArthmeticError NameError
- 4. Exception Handling Purpose of handling errors is to make program robust. It means strong. Robust program does not terminate in the middle. When there is a error displays appropriate message to the user and continue execution. When the errors can be handled they are called exception. To handle the exception the programmer should perform the following three steps Step1: The statement that may cause the exception must be written inside a ‘try’ block try: statements If statement raises an error then it enters into except block otherwise continues the execution
- 5. continued Step2:Programmer should write except block where we should display the exception details to the user except exception name: statements #these statements from handler Step3:Lastly the programmer should perform clean up actions like closing the files and terminating any other processes which are running. finally: statements Statements inside the finally block are executed irrespective of whether there is an exception or not. This ensures that all the opened files are properly closed and all the running processes are terminated properly.
- 6. Syntax for handling exception try: statements except Exception1: exception handler1 except Exception2: exception handler2 else: statements finally: statements
- 7. Types of Exception Exception Class Name Description Exception Represents any type of exception. All exception are sub classes of this class ArithmeticError Represents the base class for arithmetic errors like OverflowError, ZeroDivisionError, FloatingPointError AssertionError Raised when an assert statement gives error AttributeError Raised when an attribute reference or assignment fails EOFError Raised when input() function reaches end of file condition without reading any data FloatingPointError Raised when a floating operation fails GeneratorExit Raised when generators close() method is called IOError Raised when an input or output operation failed. It raises when the file opened is not found or when writing data disk is full ImportError Raised when an import statement fails to find the module being imported
- 8. continued Exception Class Name Description IndexError Raised when a sequence index or subscript is out of range KeyError Raised when a mapping (dictionary) key is not found in the set of existing keys KeyboardInterrupt Raised when the user hits the interrupt key(Control-C, Delete) NameError Raised when an identifier is not found locally or globally NotImplementedError Derived from runtimeError
- 9. Programs on exception Python program to handle ZeroDivisionError exception Filename:ep1.py Python program to handle syntax error given by eval() function Filename:ep2.py Python program to handle multiple exception Filename:ep3.py
- 10. User Defined Exception Like the built in exceptions of python user can also create his own exceptions which are called user defined exception or custom exception. EXAMPLE: Matainance of minimum balance in account Steps to define user defined exception 1.Create own exception class and is sub class of built in class Exception class MyExecption(Exception): def __init__(self,arg): self.msg=arg msg is member of class MyException and is assigned with parameter received from outside
- 11. Continued 2. When the programmer suspects the possibility of exception raise own exception using raise statement Raise MyExecption(‘message’) 3. Programmer must write the code inside a try block and catch the exception using except block as try: code except MyException as me print(me) Python program to illustrate user defined exception Filename:ep4.py
- 12. THANK YOU