docs: def trim_seqs(input_seqs, trim_len, left_trim_len):
      """Trim FASTA sequences to specified length.
  
      Parameters
      ----------
      input_seqs : iterable of (str, str)
          The list of input sequences in (label, sequence) format
      trim_len : int
          Sequence trimming length. Specify a value of -1 to disable trimming.
      left_trim_len : int
          Sequence trimming from the 5' end. A value of 0 will disable this trim.
  
  
      Returns
      -------
      Generator of (str, str)
          The trimmed sequences in (label, sequence) format
      """
      # counters for the number of trimmed and total sequences
      logger = logging.getLogger(__name__)
  
      okseqs = 0
      totseqs = 0
  
      if trim_len < -1:
          raise ValueError("Invalid trim_len: %d" % trim_len)
  
      for label, seq in input_seqs:
          totseqs += 1
  
          if trim_len == -1:
              okseqs += 1
              yield label, seq
          elif len(seq) >= trim_len:
              okseqs += 1
              yield label, seq[left_trim_len:trim_len]
  
      if okseqs < 0.01*totseqs:
          logger = logging.getLogger(__name__)
          errmsg = 'Vast majority of sequences (%d / %d) are shorter ' \
                   'than the trim length (%d). ' \
                   'Are you using the correct -t trim length?' \
                   % (totseqs-okseqs, totseqs, trim_len)
          logger.warn(errmsg)
          warnings.warn(errmsg, UserWarning)
      else:
          logger.debug('trimmed to length %d (%d / %d remaining)'
                       % (trim_len, okseqs, totseqs))