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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 _save_subimports(self, code, top_level_dependencies):
 """ Ensure de-pickler imports any package child-modules that are needed by the function """

        # check if any known dependency is an imported package
        for x in top_level_dependencies:
            if isinstance(x, types.ModuleType) and hasattr(x, '__package__') and x.__package__:
                # check if the package has any currently loaded sub-imports
                prefix = x.__name__ + '.'
                for name, module in sys.modules.items():
                    # Older versions of pytest will add a "None" module to sys.modules.
                    if name is not None and name.startswith(prefix):
                        # check whether the function can address the sub-module
                        tokens = set(name[len(prefix):].split('.'))
                        if not tokens - set(code.co_names):
                            # ensure unpickler executes this import
                            self.save(module)
                            # then discards the reference to it
                            self.write(pickle.POP)