def METHOD_NAME(dataframe, max_size):
  """ Returns an index to a model, based on available data."""
  for i, model in enumerate(MODELS):
    required_features = dataframe[model['required_features']]
    # A model can only make a prediction if all required features
    # are present.
    # required_features is 2D single row, so all() must be called twice.
    if required_features.notnull().all().all():
      return i
  return -1