TypeError for definied variable in python

Question

I'm trying to make a music player that allows a song to be put into the shell and is then played however, I'm having an issue with a type error in class Notes(): and I can't figure out why.

import winsound
import time

length = 125

class Notes():
    def processNote(note):
        if(note == 'C'):return Notes.processNote(262)
        if(note == 'D'):return Notes.processNote(294)
        if(note == 'D5'):return Notes.processNote(587)
        if(note == 'A'):return Notes.processNote(440)
        if(note == 'Ab'):return Notes.processNote(415)
        if(note == 'G'):return Notes.processNote(392)
        if(note == 'F'):return Notes.processNote(349)
        if(note == 'B'):return Notes.processNote(247)
        if(note == 'Bb'):return Notes.processNote(233)
song = "CCCCCCCCCCCD"
noteList = list(song)
print(noteList)

for note in noteList:
    print("Doing ", note)
    frequency = Notes.processNote(note)
    winsound.Beep(frequency, length)

The error:

Traceback (most recent call last):
  File "C:\Python\Tester.py", line 27, in <module>
    winsound.Beep(frequency, length)
TypeError: an integer is required (got type NoneType)

I believe you just mean return 262 and so on; currently you are calling your function twice, and the second time always returns None because you are passing it an integer your function only handles strings. — Aurora0001
– Aurora0001, Commented Oct 9, 2016 at 9:33

Nf4r · Accepted Answer · 2016-10-09 09:47:56Z

1

And if I can say something, instead of

class Notes():
    def processNote(note):
        if(note == 'C'):return Notes.processNote(262)
        if(note == 'D'):return Notes.processNote(294)
        if(note == 'D5'):return Notes.processNote(587)
        (thousands IFs)

You could use the python dictionary and create mapping:

class Notes():
    def processNote(note):
        signature_to_freq = {'C': 262, 'D': 294, 'D5': 587,
                            'B': 247}
        return signature_to_freq[note]

edited Oct 9, 2016 at 9:47

answered Oct 9, 2016 at 9:36

Nf4r

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2 Comments

Nf4r Over a year ago

Well it's also better (easier) to change the return of the function. Edited.

Joseph Over a year ago

Oh that's a much tidier way of writing it. I'll try to swap that in thank you.

Aurora0001 · Accepted Answer · 2016-10-09 09:37:36Z

Currently, the function processNote() returns None for any valid input, because you are calling it twice instead of just returning the value. It may be helpful to look at how your code will be processed to understand why this happens:

Imagine processNote() is called with the note value "C". That will match the first if statement and it will return the result of calling processNote() with the value 262. Since there's no if statement that catches 262 in the processNote() function, it returns None (because this is the default for Python functions), so the frequency variable ends up being None.

You can solve this rather simply, by just returning the literal value:

def processNote(note):
    if note == 'C':
        return 262
    ...

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