code: def check_initializers(initializers, keys):
    
    if initializers is None:
      return {}
    _assert_is_dictlike(initializers, valid_keys=keys)
  
    keys = set(keys)
  
    if not set(initializers) <= keys:
      extra_keys = set(initializers) - keys
      raise KeyError(
          "Invalid initializer keys {}, initializers can only "
          "be provided for {}".format(
              ", ".join("'{}'".format(key) for key in extra_keys),
              ", ".join("'{}'".format(key) for key in keys)))
  
    _check_nested_callables(initializers, "Initializer")
  
    return dict(initializers)
docs: Checks the given initializers.
  
    This checks that `initializers` is a dictionary that only contains keys in
    `keys`, and furthermore the entries in `initializers` are functions or
    further dictionaries (the latter used, for example, in passing initializers
    to modules inside modules) that must satisfy the same constraints.
  
    Args:
      initializers: Dictionary of initializers (allowing nested dictionaries) or
        None.
      keys: Iterable of valid keys for `initializers`.
  
    Returns:
      Copy of checked dictionary of initializers. If `initializers=None`, an empty
      dictionary will be returned.
  
    Raises:
      KeyError: If an initializer is provided for a key not in `keys`.
      TypeError: If a provided initializer is not a callable function, or
        `initializers` is not a Mapping.