def serialized(self):
        to_ret = {}
        for group, requirements in self.items():
            to_ret[group] = [str(requirement) for requirement in requirements]
        return to_ret
def find_files(pattern, root):
  """Return all the files matching pattern below root dir."""
  for path, _, files in os.walk(root):
    for filename in fnmatch.filter(files, pattern):
      yield os.path.join(path, filename)