code: def warn_if_nans_exist(X):
      
      null_count = count_rows_with_nans(X)
      total = len(X)
      percent = 100 * null_count / total
  
      if null_count > 0:
          warning_message = \
              'Warning! Found {} rows of {} ({:0.2f}%) with nan values. Only ' \
              'complete rows will be plotted.'.format(null_count, total, percent)
          warnings.warn(warning_message, DataWarning)
docs: Warn if nans exist in a numpy array.