text: # Copyright 2017 Google Inc.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #      http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  """Postprocessing utilities for CLIF.
  
  Example usage:
  
  For
  bool Actor(const string& input, vector<int>* output);
  use
  def Actor(input: str) -> (ok: bool, output: list<int>) with ValueErrorOnFalse
  to get clean list<int> for output and ValueError on error.
  """
  
  
  def ValueErrorOnFalse(ok, *args):
    """Returns None / arg / (args,...) if ok."""
    if not isinstance(ok, bool):
      raise TypeError("Use ValueErrorOnFalse only on bool return value")
    if not ok:
      raise ValueError("CLIF wrapped call returned False")
    # Plain return args will turn 1 into (1,)  and None into () which is unwanted.
    if args:
      return args if len(args) > 1 else args[0]
    return None
  