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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 _merge_namespace_options( namespace_set=None, ex_namespace_set=None, gridfs_set=None, dest_mapping=None, namespace_options=None, include_fields=None, exclude_fields=None, ):
 """Merges namespaces options together. The first is the set of excluded namespaces and the second is a mapping from source namespace to Namespace instances. """

    namespace_set = set(namespace_set or [])
    ex_namespace_set = set(ex_namespace_set or [])
    gridfs_set = set(gridfs_set or [])
    dest_mapping = dest_mapping or {}
    namespace_options = namespace_options or {}
    include_fields = set(include_fields or [])
    exclude_fields = set(exclude_fields or [])
    namespaces = {}

    for source_name, options_or_str in namespace_options.items():
        if isinstance(options_or_str, dict):
            namespace_set.add(source_name)
            if options_or_str.get("gridfs"):
                gridfs_set.add(source_name)
            namespaces[source_name] = Namespace(
                dest_name=options_or_str.get("rename"),
                include_fields=options_or_str.get("includeFields"),
                exclude_fields=options_or_str.get("excludeFields"),
                gridfs=options_or_str.get("gridfs", False),
            )
        elif isinstance(options_or_str, str):
            namespace_set.add(source_name)
            namespaces[source_name] = Namespace(dest_name=options_or_str)
        elif options_or_str:
            namespace_set.add(source_name)
        else:
            ex_namespace_set.add(source_name)

    # Add namespaces that are renamed but not in namespace_options
    for source_name, target_name in dest_mapping.items():
        namespaces[source_name] = namespaces.get(source_name, Namespace()).with_options(
            dest_name=target_name
        )

    # Add namespaces that are included but not in namespace_options
    for included_name in namespace_set:
        if included_name not in namespaces:
            namespaces[included_name] = Namespace()

    # Add namespaces that are excluded but not in namespace_options
    for gridfs_name in gridfs_set:
        namespaces[gridfs_name] = namespaces.get(gridfs_name, Namespace()).with_options(
            gridfs=True
        )

    # Add source, destination name, and globally included and excluded fields
    for included_name in namespaces:
        namespace = namespaces[included_name]
        namespace = namespace.with_options(
            source_name=included_name,
            include_fields=validate_include_fields(
                include_fields, namespace.include_fields
            ),
            exclude_fields=validate_exclude_fields(
                exclude_fields, namespace.exclude_fields
            ),
        )
        # The default destination name is the same as the source.
        if not namespace.dest_name:
            namespace = namespace.with_options(dest_name=included_name)
        namespaces[included_name] = namespace

    return ex_namespace_set, namespaces