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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 register_unpack_format(name, extensions, function, extra_args=None, description=''):
 """Registers an unpack format. `name` is the name of the format. `extensions` is a list of extensions corresponding to the format. `function` is the callable that will be used to unpack archives. The callable will receive archives to unpack. If it's unable to handle an archive, it needs to raise a ReadError exception. If provided, `extra_args` is a sequence of (name, value) tuples that will be passed as arguments to the callable. description can be provided to describe the format, and will be returned by the get_unpack_formats() function. """

    if extra_args is None:
        extra_args = []
    _check_unpack_options(extensions, function, extra_args)
    _UNPACK_FORMATS[name] = extensions, function, extra_args, description