code: def to_csv(weekmatrices, filename, digits=5):
      
  
      with open(filename, 'w') as f:
          w = csv.writer(f, lineterminator='\n')
          w.writerow(['year_week', 'channel', 'weekday', 'section', 'value'])
  
          def make_repr(item):
              if item is None:
                  return None
              elif isinstance(item, float):
                  return repr(round(item, digits))
              else:
                  return str(item)
  
          for row in weekmatrices:
              w.writerow([make_repr(item) for item in row])
docs: Exports a list of week-matrices to a specified filename in the CSV format.
  
      Parameters
      ----------
      weekmatrices : list
          The week-matrices to export.
      filename : string
          Path for the exported CSV file.