sample_program.py

supported = ['a', 'b',..]

def load_model(source, target):
  try:
    if source == target:
      raise AssertionError("source and target shouldn't be same")

    if( source in supported) and (target in supported):
      .....
      if source == "ta":
        raise ValueError("Not supported pair")
  except AssertionError as e:
    return {"inputerror": "Please enter required fields"}
  except ValueError as e:
    return {"error": e}

//Assume this as flask API endpoint
def predict_raw(X):
  try:
    tokenizer, model = load_model(X['s'], X['t'])
    .....
    return preds
  except Exception as e:
    return {"error": e}