CMPE-30032-Module-3-Exception-Handling-in-Python-1.pptx

CMPE 30032 Module 3 Exception Handling  TABLE OF CONTENTS 01 What are Exceptions? 02 Example of Exceptions Cases 03 Types of Exceptions 04 Handling an Unchecked Exceptions 05 Examples What is an Exception? An exception is an error that happens during execution of a program. When tha...

CMPE 30032 Module 3 Exception Handling  TABLE OF CONTENTS 01 What are Exceptions? 02 Example of Exceptions Cases 03 Types of Exceptions 04 Handling an Unchecked Exceptions 05 Examples What is an Exception? An exception is an error that happens during execution of a program. When that error occurs, Python generate an exception that can be handled, which avoids your program to crash. Why use Exceptions? Exceptions are convenient in many ways for handling errors and special conditions in a program. When you think that you have a code which can produce an error then you can use exception handling. Raising an Exception Example IOError for Exception Cases: - If the file cannot be opened. ImportError - If python cannot find the module ValueError - Raised when a function receives an argument that has the right type but an inappropriate value Types of Exceptions - Checked (Compile-time) - Checked exceptions are checked at compile-time. - Exceptions are “checked” because they are subject to the “catch” or “specify requirement” otherwise, the program code will not compile. Examples: Invalid Syntax, Incorrect statements - Unchecked (Runtime) - Unchecked exceptions are not checked at compile time. - Errors are not subject to the “catch” or “specify requirement”. Python Unchecked Exceptions SyntaxErro a=1 ZeroDivision NameEr rif a < 0 Error num = 30 result = num/0 ror print(resu print("Negati print(result) lt) ve") TypeErro num = “five” ValueError Sample input: num = int(input("Enter a rresult = number: ")) two num+5 result = num+2 print(result) print(result) Handling Unchecked Exception  try is used to test a block of code for errors  except is used to handle errors  finally is used to execute block of code regardless of the result of the try and except blocks  Exception Handling - Structure try: # Try block of Statements except : # Exception handling statements finally: # Finally block of statements Using try…except try: print(age) print(age) except: print(“Age variable is not defined") Output: print(“You must assign a value Traceback (most recent call last): first or Output: declare it") File "F:\DICTPython\Exception.py", line 1, in print(age) NameError: name 'age' is not defined Age variable is not defined You must assign a value first or declare it Print a specific error message if the try block raises a NameError try: print(age) except NameError: This statement will be print("Variable age is executed since the try not defined") block encountered a except: NameError print("Something else went wrong") Output: Variable age is not defined Else else is used to define a block of code to be executed try: if no errors were raised print("Hello World") except: print("An error occured") This statement will be else: executed since there’s print("No error") no error inside the try block Output: Hello World No error Finally finally block will be executed regardless if the try block raises an errortry: or not. try: print("Hello World") print(age) except: except: print("An error print("An error occurred") occurred") else: else: print("No error") print("No error") finally: finally: print(“Finished") print(“Finished") Output: Hello World Output: An error occurred No error Finished Finished Raise an Exception raise is used to throw an exception if a condition ageoccurs. = -1 if age < 0: raise Exception("Sorry, age is out of range") age = "30" if not type(age) is int: raise TypeError("Can accept integer value only") Exception Handling – Example 01 x = 10 y = 5 try: result = x // y print("Yeah ! Your answer is :", result) except ZeroDivisionError: print("Sorry ! You are dividing by zero ") finally: print(“End of Program")  Exception Handling – Example 02 x = -1 if x < 0: raise Exception("Sorry, no numbers below zero") Exception Handling – Example 03 x = "hello" if not type(x) is int: raise TypeError("Only integers are allowed")  Exception Handling – try:Example 04 x = int(input(“Enter the value of X : ”)) y = int(input(“Enter the value of Y : ”)) result = x / y print(“ Answer : ", result) except ZeroDivisionError: print("Sorry ! You are dividing by zero ") except ValueError: print("Sorry ! You are dividing by zero ") finally: print(“End of Program")  Exception Handling – Example 05 try: f = open("demo.txt") f.write(“Python Programming") except: print("Something went wrong when writing to the file ") finally: f.close()  Exception Handling – Example try: 06 a = 3 if a < 4 : b = a / (a-3) print( “Value of b = “, b) except(ZeroDivisionError, NameError): print( “Error Occurred and Handled” ) except: print ( “Unknown Exception” ) Exception Handling – Example 07 try: x = int(input("Enter the value of X : ")) y = int(input("Enter the value of Y : ")) print("Answer :", x / y) except ZeroDivisionError: print("Division by Zero Error") else: print("Else Block") finally: print("End of Program") Programming Exercise: Create a Simple App Calculator 1. The application will ask the user to choose one of the four math operations (Addition, Subtraction, Multiplication and Division) 2. The application will ask the user for two numbers 3. Display the result 4. The application will ask if the user wants to try again or not. 5. If yes, repeat Step 1. 6. If no, Display “Thank you!” and the program will exit 7. Use Python Function and appropriate Exceptions to capture errors during runtime.