Looking at the docs, it looks like it's an instance of ID3Tags, which appears to be based on couple of helper classes mutagen._util.DictProxy and mutagen._tags.Tags, where DictProxy (and its base DictMixin) provides the dict-like interface. Underneath that, it looks like it's storing the actual values in a simple dict (DictProxy.__dict) and proxying to that.

I'm not seeing anything obvious that would muck with the incoming lookup key anywhere in ID3Tags or DictProxy.__getitem__ or any of the other base classes.

I have to jump off to pack for a trip, but might try this out later in a live shell session to see if there's something odd going on with the API.

In the meantime, OP, are you positive you were looking at the same file each time? Was this in a script or in a live Python shell session?

I'm getting 0.66 when I do get a rating. But I'm definitely not getting that to print. Here's the full file

import os
import mutagen
import requests
import urllib.parse
from mutagen.easyid3 import EasyID3
from mutagen.id3 import ID3
from pprint import pprint

# Navidrome credentials
navidrome_url = "http://navidrome.local:4533"
navidrome_username = "your-username"
navidrome_password = "your-password"
hex_encoded_pass = navidrome_password.encode().hex()
headers = None

# Directory containing MP3 files
mp3_directory = "/nfs"

def extract_rating(mp3_file):
    global rating
    audio = mutagen.File(mp3_file)
    tags = ID3(mp3_file)

    print(tags["TXXX:FMPS_Rating_AMarok_Score"]) #Gives KeyError

    for frame in tags.getall("TXXX"):
      rating = frame #This is terrible. The last key is the rating and since I can't call it by the key, I'm just refilling the variable
      print(rating)

# It was moaning about strings and floats, so commented out
#    if rating >= 1.0:
#      return 5
#    elif rating >= 0.8:
#      return 4
#    elif rating >= 0.6:
#      return 3
#    elif rating >= 0.4:
#      return 2
#    elif rating >= 0.2:
#      return 1
#    else:
#      return 0

#    return rating

def update_rating_on_navidrome(track_id, rating):
    url = f"{navidrome_url}/rest/setRating?id={track_id}&u={navidrome_username}&p=enc: {hex_encoded_pass}&v=1.12.0&rating={rating}"
    data = {"rating": rating}
    response = requests.get(url, headers=headers, json=data)

def find_track_id_on_navidrome(mp3_file):
    url = urllib.parse(url)
    url = f"{navidrome_url}/rest/getSong?path={mp3_file.encode()}&u={navidrome_username}&p=enc: {hex_encoded_pass}&v=1.12.0"
    response = requests.get(url, headers=headers, json=data)
    return url[track_id]

    if response.status_code == 204:
        print(f"Rating updated successfully for track {track_id}")
    else:
        print(f"Failed to update rating for track {track_id}: {response.text}")

print("hello")
#test = 
print(os.listdir(mp3_directory))

for foldername in os.listdir(mp3_directory):
  folderpath = "/".join([mp3_directory, foldername])
  for filename in os.listdir(folderpath):
    if filename.endswith(".mp3"):
        mp3_file = "/".join([folderpath, filename])
        rating = extract_rating(mp3_file)
        print(mp3_file, rating, sep= "_____")
        print(rating)
#
#        # Implement logic to find the track ID on Navidrome based on filename or other metadata
#        track_id = find_track_id_on_navidrome(filename)  # Replace with your implementation#
#
#        if track_id:
#            update_rating_on_navidrome(track_id, rating)
#        else:
#            print(f"Track ID not found on Navidrome for {filename}")

Have I called something erroneously that would mess it up?

Sorry if it's terrible to read, up until I started trying to do this, I had never touched Python before and haven't attempted to code for years.