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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_comic_format(filename):
 """Return the comic format if it is a comic archive."""

    image_format = None
    filename_ext = os.path.splitext(filename)[-1].lower()
    if filename_ext in _COMIC_EXTS:
        if zipfile.is_zipfile(filename):
            image_format = _CBZ_FORMAT
        elif rarfile.is_rarfile(filename):
            image_format = _CBR_FORMAT
    return image_format