morse.py is the same as in the previous exercise. We have our test in Message.__init__ to check for !:

letter_to_morse = {
    'a':'.-', 'b':'-...', 'c':'-.-.', 'd':'-..', 'e':'.', 'f':'..-.', 
    'g':'--.', 'h':'....', 'i':'..', 'j':'.---', 'k':'-.-', 'l':'.-..', 'm':'--', 
    'n':'-.', 'o':'---', 'p':'.--.', 'q':'--.-', 'r':'.-.', 's':'...', 't':'-',
    'u':'..-', 'v':'...-', 'w':'.--', 'x':'-..-', 'y':'-.--', 'z':'--..',
    '0':'-----', '1':'.----', '2':'..---', '3':'...--', '4':'....-',
    '5':'.....', '6':'-....', '7':'--...', '8':'---..', '9':'----.', ' ':'/'
}


def encode(message):
    if "!" in message:                                            # ← new code
        raise ValueError(f"'!' is not valid in English strings")  # ←
    
    morse = []

    for letter in message:
        letter = letter.lower()
        morse_letter = letter_to_morse[letter]
        morse.append(morse_letter)

    morse_message = " ".join(morse)
    
    return morse_message


# We need to invert the dictionary. This will create a dictionary
# that can go from the morse back to the letter
morse_to_letter = {}
for letter in letter_to_morse:
    morse = letter_to_morse[letter]
    morse_to_letter[morse] = letter


def decode(message):
    english = []

    morse_letters = message.split(" ")

    for letter in morse_letters:
        english_letter = morse_to_letter[letter]
        english.append(english_letter)

    english_message = "".join(english)
    
    return english_message

If we add some ! to our message_string in encode.py then we see our ValueError exception raised:

import morse

message = "SOS We have hit an iceberg and need help quickly!!!!!"  # ← Added ! to end of string

encoded_message = morse.encode(message)

print(f"Incoming message: {message}")
print(f"   Morse encoded: {encoded_message}")

python encode.py

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
~/projects/courses/intermediate_python/encode.py in <module>
      4 message = "SOS We have hit an iceberg and need help quickly!!!!!"  # ← Added ! to end of string
      5 
----> 6 encoded_message = morse.encode(message)
      7 
      8 print(f"Incoming message: {message}")

~/projects/courses/intermediate_python/morse.py in encode(message)
     12 def encode(message):                                              # ←
     13     if "!" in message:                                            # ← new code
---> 14         raise ValueError(f"'!' is not valid in English strings")  # ←
     15 
     16     morse = []

ValueError: '!' is not valid in English strings

Moving all that code into a try/except ValueError block we can catch the error and print something

import morse

message = "SOS We have hit an iceberg and need help quickly!!!!!"

try:
    encoded_message = morse.encode(message)

    print(f"Incoming message: {message}")
    print(f"   Morse encoded: {encoded_message}")
except ValueError as e:
    print(f"Could not encode message: {e}")

python encode.py

Could not encode message: '!' is not valid in English strings

Passing in a valid string (removing the !) results in the code running correctly:

import morse

message = "SOS We have hit an iceberg and need help quickly"  # Removed ! from end of string

try:
    encoded_message = morse.encode(message)

    print(f"Incoming message: {message}")
    print(f"   Morse encoded: {encoded_message}")
except ValueError as e:
    print(f"Could not encode message: {e}")

python encode.py

Incoming message: SOS We have hit an iceberg and need help quickly
   Morse encoded: ... --- ... / .-- . / .... .- ...- . / .... .. - / .- -. / .. -.-. . -... . .-. --. / .- -. -.. / -. . . -.. / .... . .-.. .--. / --.- ..- .. -.-. -.- .-.. -.--

Intermediate Python