U3M3A3.1

#Ayden Finch #11/15/20 #U3 M3 A3.1 #I learned how to handle errors using try, ecxept, else, and finally.

lst = [0, 1, 2] print(lst[30])

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# x is not defined anywhere print(x)

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s1 = 'Word1' s2 = 'Word2' s1/s2

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# [ ] Write an expression to raise a `ModuleNotFoundError` exception import ayden

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# [ ] Write an expression to raise an `ImportError` exception from math import datetime

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try: 5/0 except ZeroDivisionError: print("Cannot divide by zero!") print("Program is still running")

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lst = ['text', 5, 12] for i in range(5): try: print(lst[i] / i) print("print executed") except TypeError: print("Cannot divide strings") except IndexError: print("Cannot access out of range elements")

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# Without handling unexpected exception x = [5] try: x / 0 except ZeroDivisionError: print("Cannot divide by zero!")

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# Handling unexpected exception x = [5] try: x / 0 except ZeroDivisionError: print("Cannot divide by zero!") except: print("Unexpected error")

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old_lst = [6, 'word', [2, 5], 0, 3] new_lst = [] for i in range(6): try: tmp = 12 / old_lst[i] new_lst.append(tmp) print("List appended with", tmp) except TypeError: print("Cannot divide {0:d} by {1:}".format(12, type(old_lst[i]))) except ZeroDivisionError: print("Cannot divide by 0") # Handling unexpected exceptions, by showing the associated error message except Exception as exception_object: print("Unexpected error: {0:}".format(exception_object)) print() print("The new list is:", new_lst)

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# Without exception handling from math import sqrt x = -3 sqrt(x)

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# With exception handling from math import sqrt x = -3 try: sqrt(x) except ValueError as exception_object: # Storing the error message in exception_object print(exception_object)

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# [ ] The following program adds `lst1` to `lst2` element by element # Find all exceptions that will be generated by this program, # then handle the exceptions by displaying meaningful messages. # You should also handle unexpected exceptions. lst1 = [-4, -5, 6, [6], "hello"] lst2 = [ 5, 16, [6], "hello", "goodbye"] for i in range(7): try: print(lst1[i] + lst2[i]) except TypeError: print("Cannot do: {} + {}".format(type(lst1[i]),type(lst2[i]))) except ZeroDivisionError: print("index out of range") except Exception as exception_object: print(exception_object) print("Done!")

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# [ ] The following program asks the user for an integer then prints the result of dividing it by 2. # If the user enters an invalid value (i.e. "4.3" or "Hello"), the program terminates. # Use exception handling to deal with unexpected user input and display a meaningful message. x = input("Enter an integer: ") try: x = int(x) print("{:d} / 2 = {:.2f}".format(x, x / 2)) except Exception as exception_object: print(exception_object) print("Done!")

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x = 3 y = 2 try: print(x/y) except ZeroDivisionError: print("Cannot divide by zero") else: print("All good! No exceptions were raised.")

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x = 3 y = 2 try: print(x/y) except ZeroDivisionError: print("Cannot divide by zero") finally: print("Code that will run whether an exception was raised or not")

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x = 3 y = 0 try: print(x/y) except ZeroDivisionError: print("Cannot divide by zero") finally: print("Code that will run whether an exception was raised or not")

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# [ ] The following program asks the user for an integer `x` then assigns `y` as the result of dividing `x` by 2. # If the user enters an invalid value (i.e. "4.3" or "Hello"), the program terminates. # Use exception handling to deal with unexpected user inputs, then use an `else` clause to calculate the value of `y`. x = input("Enter an integer: ") y = None try: x = int(x) except Exception as exception_object: print(exception_object) else: y = x / 2; if y is not None: print("No exceptions were raised, you can use y =", y) else: print("An exception was raised, y cannot be used")

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# [ ] The following program tries to write to a file opened for reading. # The program will terminate before closing the file, and the file resources will not be released. # Use exception handling with a `finally` clause to make sure the file is closed. # Open a text file for reading f = open("parent_dir/text_file.txt", 'r') try: # Try to write to a file open for reading (will raise an exception) f.write("This string will not be written") # Close the file (will not be reached if an exception was raised) f.close() print("File closed")

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valid = False while not valid: try: x = int(input("Enter a number between 1 and 10: ")) if ((x < 1) or (x > 10)): raise ValueError("The number is outside of the acceptable range") valid = True except ValueError as except_object: print("{}".format(except_object)) print("{:d} was accepted".format(x))

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def isValid(num): if ((num < 1) or (num > 10)): raise ValueError("The number is outside of the acceptable range") else: return num valid = False while not valid: try: x = int(input("Enter a number between 1 and 10: ")) x = isValid(x) valid = True except ValueError as except_object: print("{}".format(except_object)) print("{:d} was accepted".format(x))

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# [ ] Write a program to keep prompting the user for an odd positive number until a valid number is entered. # Your program should raise an exception with an appropriate message if the input is not valid. valid = False while not valid: try: x = int(input("Enter an odd positive number: ")) if ((x < 0) or (x % 2 == 0)): raise ValueError("Number is not valid") valid = True except ValueError as except_object: print("{}".format(except_object)) print("{:d} was accepted".format(x))

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# [ ] Complete the function `isValid` to test the validity of a user input. A valid input should be an odd positive integer. # The function should raise an exception with an appropriate message if the input is not valid. # The function need not handle the exception. def isValid(num): if ((num < 0) or (num % 2 == 0)): raise ValueError("The number is outside of the acceptable range") else: return num pass valid = False while not valid: try: x = int(input("Enter an odd positive number: ")) x = isValid(x) valid = True except ValueError as except_object: print("{}".format(except_object)) print("{:d} was accepted".format(x))

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