Mutagen MP3 Image Error

add.py

def add_image(
  filenames, image_path, description='Cover', img_type=3, encoding=3
):
  """
  Adds an image to MP3 from *filenames*.

  Args:

    filenames (lits): paths to the MP3
    image_path (string): path to image file
    description (string): optional description
    img_type (integer): ID3 code for the iomage (3=cover)
    encoding (integer): encoding to use (3=UTF-8)

  Raises:

    ArgumentError: on *image_path* errors

  Image Type:

    https://mutagen.readthedocs.org/en/latest/api/id3.html#mutagen.id3.PictureType

  Encoding:

    https://mutagen.readthedocs.org/en/latest/api/id3.html#mutagen.id3.Encoding

  """
  SUPPORTED_TYPES = (
    '.png',
    '.jpg', '.jpeg',
  )
  # check image
  if not os.path.exists(image_path):
    msg = "the image seems not to exists: '{}'"
    msg = msg.format(image_path)
    raise ArgumentError(msg)
  img_type = os.path.splitext(image_path)[1].lower()
  if img_type not in SUPPORTED_TYPES:
    msg = "image type '{}' is not supported, only: {}"
    msg = msg.format(img_type, ', '.join(SUPPORTED_TYPES))
    raise ArgumentError(msg)
  if img_type == 'png':
    mime = 'image/png'
  else:
    mime = 'image/jpeg'
  # add image to files
  image = open(image_path, mode='rb').read()
  image = APIC(
    encoding=encoding,
    mime=mime,
    type=img_type,
    desc=description,
    data=image
  )
  for filename in filenames:
    print("- {}".format(filename))
    mp3 = MP3(filename, ID3=ID3)
    # add image tag
    mp3.tags.add(image)
    mp3.save()

error.py

Traceback (most recent call last):
  File "~/.local/bin/mp3tag", line 190, in <module>
    sys.exit(main())
  File "~/.local/bin/mp3tag", line 183, in main
    add_image(args.filenames, args.image)
  File "~/.local/bin/mp3tag", line 124, in add_image
    data=image
  File "~/.local/lib/python3.4/site-packages/mutagen/id3/_frames.py", line 69, in __init__
    self, kwargs.get(checker.name, None))
  File "~/.local/lib/python3.4/site-packages/mutagen/id3/_specs.py", line 130, in validate
    chr_(value)
  File "~/.local/lib/python3.4/site-packages/mutagen/_compat.py", line 64, in <lambda>
    chr_ = lambda x: bytes([x])
TypeError: 'str' object cannot be interpreted as an integer