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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 _list_files(path, suffix=""):
 """ Returns a list of all files ending in `suffix` contained within `path`. Parameters path : str a filepath suffix : str Returns ------- l : list A list of all files ending in `suffix` contained within `path`. (If `path` is a file rather than a directory, it is considered to "contain" itself) """

  if os.path.isdir(path):
    incomplete = os.listdir(path)
    complete = [os.path.join(path, entry) for entry in incomplete]
    lists = [_list_files(subpath, suffix) for subpath in complete]
    flattened = []
    for one_list in lists:
      for elem in one_list:
        flattened.append(elem)
    return flattened
  else:
    assert os.path.exists(path), "couldn't find file '%s'" % path
    if path.endswith(suffix):
      return [path]
    return []