docs: def validate_sample_frame(sample_frame):
      """Makes sure that `sample_frame` has the columns we expect.
  
      :param DataFrame sample_frame: A sample data frame.
      :return: True (or raises an exception)
      :raises TypeError: if sample_frame is not a pandas DataFrame
      :raises ValueError: if columns are missing or the wrong type
      """
      if not isinstance(sample_frame, pd.core.frame.DataFrame):
          raise TypeError("Expected a pandas DataFrame, received {}".format(type(sample_frame)))
      for col in ['Sample', 'Target', 'Cq']:
          if col not in sample_frame:
              raise ValueError("Missing column {} in sample frame".format(col))
      if sample_frame['Cq'].dtype.kind != 'f':
          raise ValueError("Expected Cq column to have float type; has type {} instead".format(str(sample_frame['Cq'].dtype)))
      return True