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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 needed_inputs(self):
 """ List all the needed inputs of a configured engine ['in'] But now if we unactivate the first component: ['middle'] More complex example: True Note that by default the needed input is 'input': ['input'] """

        needed = set()
        available = set()       # set of available data
        for bnum, block in enumerate(self):
            if not block.selected():    # if the block will not be used
                continue
            if block.in_name is not None:
                for in_name in block.in_name:
                    if not in_name in available:
                        needed.add(in_name)
            elif bnum == 0:
                # if the first block
                needed.add(Engine.DEFAULT_IN_NAME)
            # register the output
            available.add(block.out_name)
        return needed