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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_file_contents(filename: str = None, blob: bytes = None) -> bytes: """ Returns the binary contents of a file, or of a BLOB. """

    if not filename and not blob:
        raise ValueError("no filename and no blob")
    if filename and blob:
        raise ValueError("specify either filename or blob")
    if blob:
        return blob
    with open(filename, 'rb') as f:
        return f.read()