code: def _get_flowcell_id(in_file, require_single=True):
      
      fc_ids = set([x[0] for x in _read_input_csv(in_file)])
      if require_single and len(fc_ids) > 1:
          raise ValueError("There are several FCIDs in the same samplesheet file: %s" % in_file)
      else:
          return fc_ids
docs: Retrieve the unique flowcell id represented in the SampleSheet.