pySimpleUserRegAndLogin

# User Registration And Login Example
# Mike Kerry - June 2021

# Note: In this simple example, actual passwords are stored in the user details file
# In a real-world situation, actual passwords would not be stored, only password hashes

# Example of user_details text file:-
# Mike,abc123
# Fred,fredpass

userdict = {}       # This dictionary will hold User IDs and Passwords read from the user_details file and from user input

while True:
    try:
        fin = open("user_details.txt")
    except:
        break                   # user_detais.txt does not exist. Start a new user dictionary

    for uline in fin:               # Read 1 line of user-details
        uline = uline.strip()       # Remove End-of-Line characters
        usplit = uline.split(",")   # split line on comma
        userid = usplit[0]          # Get the UserID
        userpswd = usplit[1]        # Get the User Password
        if userid in userdict:      # Check this User ID does not exist already
            print("Duplicate user on file:", userid)
        else:
            userdict[userid] = userpswd     # Create a dictionary entry for this user
    fin.close()
    break

while True:                 # Main Menu Loop
    while True:                 # Loop looking for valid menu option
        print("\nMenu")
        print("1: Register new user")
        print("2. Log in existing user")
        print("8. Show all users and passwords")            # (Should be an Administrator option only)
        print("9: Quit")
        option = input("Choose option: ")
        if option in ["1", "2", "8", "9"]:
            break
        print("Invalid input")

    if option == "1":           # Register new user
        while True:             # Keep looping until a valid new User ID is entered
            userid = input("Enter user ID: ")
            if len(userid) > 12:
                print("User ID must not be longer than 12 characters")
                continue
            if userid not in userdict:              # Check User ID not already on the system
                break
            print("Sorry, that user ID already exists\n")
            # Loop around asking for a User ID

        while True:         # Keep looping until a valid password is chosen
            userpswd = input("Choose a password: ")
            if len(userpswd) > 5 and "," not in userpswd:
                break
            print("Passwords must be 6 characters or more and may not include a comma")

        userdict[userid] = userpswd         # Add new user+password to the dictionary
        print("Congratulations. User", userid, "is now registered")
        print("You may now use option 2 to Log In to the system")
        input("Press Enter to continue")

    elif option == "2":         # Log-in an existing user
        userid = input("Enter user ID: ")
        if userid in userdict:          # Check that the User ID exists in our dictionary
            userpswd = input("Enter password: ")        # Request password
            if userpswd == userdict[userid]:            # Check password matches the one held on file
                print("You have successfully logged in as", userid)
                #
                # HERE THE LOGGED IN USER CAN DO OTHER PROCESSES
                #
                input("Press Enter to continue")
                continue
        print("Invalid user ID or password")

    elif option == "8":         # Print a list of User IDs and Passwords
        # Obviously, in practice, this option would only be accessible by Admin
        sortkeys = sorted(userdict.keys())
        for userid in sortkeys:
            print(userid.ljust(16), userdict[userid])

    elif option == "9":         # Quit. Write updated dictionary to text file
        fout = open("user_details.txt", "w")
        for userid in userdict:
            # Write out UserID and Password separated by a comma, and end with New-Line
            fout.write(userid + "," + userdict[userid] + "\n")
        fout.close()
        break                   # Break out of main menu loop, so that the program terminates
print("Goodbye")