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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 is_config_file(filename, extensions=['.yml', '.yaml', '.json']):
 """ Return True if file has a valid config file type. Parameters filename : str filename to check (e.g. ``mysession.json``). extensions : str or list filetypes to check (e.g. ``['.yaml', '.json']``). Returns ------- bool """

    extensions = [extensions] if isinstance(extensions, string_types) else extensions
    return any(filename.endswith(e) for e in extensions)