Best practices in software engineering

# A lookup dictionary which, given a letter will return the morse code equivalent
_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':'----.',
                   ' ':'/'}

# 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 encode(message):
    """
    Encode a message from English to Morse Code
    
    Args:
        message (str): the English message to encode
    
    Returns:
        str: The encoded message
    
    Examples:
        >>> encode("Help us")
        ".... . .-.. .--. / ..- ..."
    """
    morse = []

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

    # We need to join together Morse code letters with spaces
    morse_message = " ".join(morse)
    
    return morse_message


def decode(message):
    """
    Decode a message from Morse Code to English
    
    Args:
        message (str): the Morse Code message to decode
    
    Returns:
        str: The decoded English message
    
    Examples:
        >>> encode(".... . .-.. .--. / ..- ...")
        "help us"
    """
    english = []

    # Now we cannot read by letter. We know that morse letters are
    # separated by a space, so we split the morse string by spaces
    morse_letters = message.split(" ")

    for letter in morse_letters:
        english.append(_morse_to_letter[letter])

    # Rejoin, but now we don't need to add any spaces
    english_message = "".join(english)
    
    return english_message