I am trying to create a dictionary of all mp3 files where the key is the mp3 filename and the value is the filepath for that file.

I do:

```
for root, dirs, files in os.walk(rootDir, topdown='true'):
    source_files_now = {filename:root for filename in files if filename[-4] == '.mp3'}
    print(source_files_now);

```

But the dictionary, source\_files\_now ends up being empty.

There are definetly mp3 files in the directory.

Any ideas?