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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 propagate_defaults(config_doc):
 """ Propagate default values to sections of the doc. """

    for group_name, group_doc in config_doc.items():
        if isinstance(group_doc, dict):
            defaults = group_doc.get('defaults', {})

            for item_name, item_doc in group_doc.items():
                if item_name == 'defaults':
                    continue
                if isinstance(item_doc, dict):

                    group_doc[item_name] = \
                        dict_merge_pair(copy.deepcopy(defaults), item_doc)

    return config_doc