Question

Write a python program that keeps names and email addresses in a dictionary as key-value pairs. The program should display a menu that lets the user look up a person’s email address, add a new name and email address, change an existing email address, and delete an existing name and email address. The program should bind the dictionary and save it to a file when the user exits the program. Each time the program starts, it should retrieve the dictionary from the file and unbind it. The program should run continuously until the user selects option exit from the menu. You can also explore using Python pickle library.

• Make some comments to explain your work please.

Answer 1

def add_contact(): #Add Contact function.In order to add a contact
                    
    print("\nAdd Contact\n")
    import pickle #Pickle module
    try: #Tries to open binary file. Carries out commands for existing dict.
        contact_file = open("Contacts.dat","rb") #Load binary
        contact_set = pickle.load(contact_file) #Load dictionary
        contact_file.close() #Securing file closure
        contact = input("Enter contact name: ") #Contact name
        email = input("Enter e-mail: ") #Contact e-mail
        contact_set.update({contact : email})
        contact_file = open("Contacts.dat","wb") #Load binary for update.
        pickle.dump(contact_set,contact_file) #Updated binary.
        contact_file.close() #Closure.
    except: #if no binary file exists
        print("You have no existing contacts!")
        contact = input("Enter contact name: ")
        email = input("Enter e-mail: ")
        contact_set = {}
        contact_set.update({contact : email})
        contact_file = open("Contacts.dat","wb") #Writes updated dictionary                                               
        pickle.dump(contact_set,contact_file)     #to binary file.
        contact_file.close()
        return


def check_list(): #Call it a 'background function'.Checks for existing file/dictionary.
    import pickle
    try:
        contact_file = open("Contacts.dat","rb")
        contact_set = pickle.load(contact_file)
        contact_file.close()
        if contact_set == {}: #if no dictionary exists
                print("You have no contacts!")
                add = input("Do you want to add a contact? ")
                if 'yes' in add.lower():
                    add_contact() #Return to the contact_add function
                else:
                    return
        else:
            return contact_set
    except EOFError: #Response to empty binary or reading error.
        print("You have no contacts!")
        add = input("Do you want to add a contact? ")
        if 'yes' in add.lower():
            add_contact()
        else:
            return
    except FileNotFoundError: #Response if no binary exists.
        print("You have no contacts!")
        add = input("Do you want to add a contact? ")
        if 'yes' in add.lower():
            add_contact()
        else:
            return

    
def search_contact(): #Function to search contacts.
    print("\nSearch Contact\n")
    import pickle
    contact_set = check_list() #File/dictionary check
    if contact_set == None: #Function break condition
        return
    else:
        try:
            search_name = input("Enter contact name, or 'All' ")
            if search_name.lower() == 'all':
                for key, value in sorted(contact_set.items()): #Attempts to
                    print("Name: ", key, "\nEmail:", \
                          value,"\n")                           #print a list of contact names and email
                return                                          
            else:
                print("Name: ", search_name, "\nEmail:", \
                      contact_set[search_name])
                return
        except KeyError: #Response for invalid entry.
            print("Entry does not exist!")
            show_list = input("Would you like to check your list? ")
            if 'yes' in show_list.lower():
                for key, value in sorted(contact_set.items()):
                    print("Name: ", key, "\nEmail:", \
                          value,"\n")
            else:
                return

    
def edit_contact(): #Function to edit contacts.
    print("\nEdit Contact\n")
    import pickle
    contact_set = check_list() #Check
    if contact_set == None:
        return
    else:
        edit = input("Enter contact name ") #User-specified name
        if edit not in contact_set: #for non-existing contact.
            create = input("Contact not in list. Create new contact? ")
            if 'yes' in create.lower():
                new_email = input("Enter e-mail: ")
                contact_set[edit] = new_email #creates new contact and email values.
                print("Name:     ", edit, "\nEmail:", \
                contact_set[edit])
                contact_file = open("Contacts.dat","wb")
                pickle.dump(contact_set,contact_file) #Update binary.
                contact_file.close()
                return
            else:
                return
        else: #for existing contact.
            new_email = input("Enter new e-mail: ")
                contact_set[edit] = new_email #Updates key with new value.
                print("Name:     ", edit, "\nNew Email:", \
                contact_set[edit])
                contact_file = open("Contacts.dat","wb")
                pickle.dump(contact_set,contact_file)
                contact_file.close()
                return
                

def delete_contact(): #Function to delete contacts.
    print("\nDelete Contact\n")
    import pickle
    contact_set = check_list() #Check
    if contact_set == None:
        return
    else:
        try:
            delete = input("Enter contact name: ")
        
            contact_set.pop(delete) #Deletion of key/value from dictionary.
            print(delete,"has been deleted from your list.")
            contact_file = open("Contacts.dat","wb")
            pickle.dump(contact_set,contact_file) #Update binary
            contact_file.close()
            if contact_set == None: #Quick break from function.
                print("No contacts found.")
            else:
                return
        except KeyError: #In case of invalid input.
            print("Entry does not exist!")
            show_list = input("Do you want to to check your list? ")
            if 'yes' in show_list.lower():
                for key, value in sorted(contact_set.items()):
                    print("Name: ", key, "\nEmail:", \
                          value,"\n")
            else:
                return


def main_menu(): #Main Menu function         
    select = ""   
    while select.lower() != "quit":       #until the value of select is not "quit",continue the program                      
        print("\nMain Menu\n")           
        select = input("Choose an option (Number or Name):\n" #menu for the user
                          "1. Add Contact\n"
                          "2. Search Contact\n"
                          "3. Edit Contact\n"
                          "4. Delete Contact\n"
                          "5. Quit\n\n")
        if select.lower() in "1. add contact": #if select is 1 or add contact
            add_contact()
        elif select.lower() in "2. search contact":#if select is 2 or search contact
            search_contact()
        elif select.lower() in "3. edit contact":#if select is 3 or edit contact
            edit_contact()
        elif select.lower() in "4. delete contact":#if select is 4 or delete contact
            delete_contact()
        elif select.lower() in "5. quit":
            break
        else:
            print("Invalid input.")
        
        
main_menu()

Here's a preview of the output

Comment in case of any doubts.