docs: def _guess_seqtype_from_file(handle):
      "Guess the sequence type from the file's contents"
      if isinstance(handle, basestring):
          handle = StringIO(handle)
  
      for line in handle:
          if not line.strip():
              continue
          if line.lstrip().split()[0] in ('LOCUS', 'FEATURES', 'source', 'CDS',
                                          'gene'):
              return 'genbank'
          if len(line) > 2 and line[:3] in ('ID ', 'FT '):
              return 'embl'
          if line.startswith('>'):
              return 'fasta'
      handle.seek(0)
      import string
      from Bio.Data import IUPACData as iupac
      all_input_letters = set(handle.read().lower())
      all_valid = set(string.digits)
      all_valid.update(set(iupac.protein_letters.lower()))
      all_valid.update(set(iupac.unambiguous_dna_letters.lower()))
      all_valid.update(set('- \n'))
      if all_valid.issuperset(all_input_letters):
          return 'fasta'
  
      raise ValueError("Failed to guess format for input")