code: def alignment_length(cigar_units):
      """Computes the span in basepairs of the cigar units.
  
      Args:
        cigar_units: iterable[CigarUnit] whose alignment length we want to compute.
  
      Returns:
        The number of basepairs spanned by the cigar_units.
      """
      return sum(
          unit.operation_length
          for unit in cigar_units
          if unit.operation in REF_ADVANCING_OPS
      )
  
file_path: deepvariant/third_party/nucleus/util/cigar.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import re
  import six
  from third_party.nucleus.protos import cigar_pb2
label_desc: Use image node_id 3 for calling a global function with example usage: alignment_length(cigar_units) and returns: sum