code: def best_assemblyfile(self):
          
          for sample in self.metadata:
              # Set the name of the unfiltered spades assembly output file
              assembly_file = os.path.join(sample.general.spadesoutput, 'contigs.fasta')
              if os.path.isfile(assembly_file):
                  sample.general.bestassemblyfile = assembly_file
              else:
                  sample.general.bestassemblyfile = 'NA'
              # Set the name of the filtered assembly file
              filteredfile = os.path.join(sample.general.outputdirectory, '{}.fasta'.format(sample.name))
              # Add the name and path of the filtered file to the metadata
              sample.general.filteredfile = filteredfile
docs: Determine whether the contigs.fasta output file from SPAdes is present. If not, set the .bestassembly
          attribute to 'NA'