code: def get_sequence_lengths(fastafilenames):
      
      tot_lengths = {}
      for fn in fastafilenames:
          tot_lengths[os.path.splitext(os.path.split(fn)[-1])[0]] = \
              sum([len(s) for s in SeqIO.parse(fn, 'fasta')])
      return tot_lengths
docs: Returns dictionary of sequence lengths, keyed by organism.
  
      Biopython's SeqIO module is used to parse all sequences in the FASTA
      file corresponding to each organism, and the total base count in each
      is obtained.
  
      NOTE: ambiguity symbols are not discounted.