What does NoneType actually mean?

Question

I have been making a morse code translator and I have just arrived at a problem with translating from morse. Here is my code:

def translate(self, message):
    message_words = message.split('   ')
    message_in_morse = ['Your message is: ']
    letters = {'.-':'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', '.----':'1', '..---':'2', '...--':'3', '....-':'4', '.....':'5', '-....':'6', '--...':'7', '---..':'8', '----.':'9', '-----':'0', '..--..':'?', '.-.-.-':'.', '--..--':',', '   ':' ', ' ':''}
    morse_text = ''
    for letter in message_words:
        message_in_morse.append(letters.get(letter.lower()))
        message_in_morse.append(' ')
    try:
        morse_text = ''.join(message_in_morse)
    except Exception as e:
        print('Error: ', str(e))
    return morse_text

I am importing it and running translate('.- .-') from another program. This should output: Your message is: aa When I run this, it just says: Error: sequence item 1: expected str instance, NoneType found I don't know what this means or how to fix it.

`letters.get` returns `None` when the key is not found in the dict, you append it to the list and that's what's causing the exception later. — bereal, Jul 07 '21 at 11:36
Use a default value in case the letter is not found: `message_in_morse.append(letters.get(letter.lower(), ''))` additionally you can get rid of the `try/except` block. — Maurice Meyer, Jul 07 '21 at 11:40
I tried this and ran it. It didn't give an error message, but it didn't give any output either, except `Your message is:` — Pazzel, Jul 07 '21 at 11:47
@Pazzel: Yes. `message.split(' ')` ... there aren't 4 blancs in `message` ... — Maurice Meyer, Jul 07 '21 at 11:55

quamrana · Answer 1 · 2021-07-08T09:24:05.997

0

Your try/except confused me for a while.

Still, I managed to find your typo:

def translate(self, message):
    message_words = message.split(' ')  # split by one space
    message_in_morse = ['Your message is: ']
    letters = {'.-':'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', '.----':'1', '..---':'2', '...--':'3', '....-':'4', '.....':'5', '-....':'6', '--...':'7', '---..':'8', '----.':'9', '-----':'0', '..--..':'?', '.-.-.-':'.', '--..--':',', '   ':' ', ' ':''}
    morse_text = ''
    for letter in message_words:
        message_in_morse.append(letters.get(letter.lower()))
    try:
        morse_text = ''.join(message_in_morse)
    except Exception as e:
        print('Error: ', str(e))
    return morse_text
print(translate('.- .-'))

Output:

Your message is: aa

Also, you should try to allow for invalid morse:

message_in_morse.append(letters.get(letter.lower(), '#'))

This will give # for any unknown morse code.

Update: removed the extra space between decoded characters.

edited Jul 08 '21 at 09:24

answered Jul 07 '21 at 11:51

quamrana

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This is like a similar comment. It just outputs `Your message is: # ` when I run it with a space in my morse code. – Pazzel Jul 07 '21 at 11:59
1

But that wasn't your question. You wanted 'a a' as the output and I fixed that problem – quamrana Jul 07 '21 at 12:29
I wanted to translate .- .-, which should give me aa. Now it gives me # – Pazzel Jul 08 '21 at 07:56
With my code I get `Your message is: a a`. – quamrana Jul 08 '21 at 08:44
It works for me like that too now, but it should still give `Your message is: aa`, not `Your message is: a a`. – Pazzel Jul 08 '21 at 09:21
Ok, but that's what your code was built to do. I'll put in a fix for that too. . . . – quamrana Jul 08 '21 at 09:23

Pazzel · Answer 2 · 2021-07-27T16:21:42.487

I've discovered how to get it to work. Use nested for loops to split the message into words, then each word gets split into separate letters.

        message_words = message.split('   ')
        letters_in_message = []
        for word in message_words:
            letters_in_message.append(word.split(' '))
        message_in_morse = ['Your message: ']
        letters = {'.-':'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', '.----':'1', '..---':'2', '...--':'3', '....-':'4', '.....':'5', '-....':'6', '--...':'7', '---..':'8', '----.':'9', '-----':'0', '..--..':'?', '.-.-.-':'.', '--..--':',', '   ':' ', ';':' '}
        morse_text = ''
        for word in letters_in_message:
            for letter in word:
                message_in_morse.append(letters.get(letter.lower(), '#'))
            message_in_morse.append(' ')
        morse_text = ''.join(message_in_morse)
        return morse_text

What does NoneType actually mean?

2 Answers2