docs: def ensure_directory_exists(dirname, context=None):
      """
      Ensures that a directory exits.
      If it does not exist, it is automatically created.
      """
      real_dirname = dirname
      if context:
          real_dirname = realpath_with_context(dirname, context)
      if not os.path.exists(real_dirname):
          os.makedirs(real_dirname)
      assert os.path.exists(real_dirname), "ENSURE dir exists: %s" % dirname
      assert os.path.isdir(real_dirname),  "ENSURE isa dir: %s" % dirname