code: def children_bp(self, feature, child_featuretype='exon', merge=False,
                      ignore_strand=False):
          
  
          children = self.children(feature, featuretype=child_featuretype,
                                   order_by='start')
          if merge:
              children = self.merge(children, ignore_strand=ignore_strand)
  
          total = 0
          for child in children:
              total += len(child)
          return total
docs: Total bp of all children of a featuretype.
  
          Useful for getting the exonic bp of an mRNA.
  
          Parameters
          ----------
  
          feature : str or Feature instance
  
          child_featuretype : str
              Which featuretype to consider.  For example, to get exonic bp of an
              mRNA, use `child_featuretype='exon'`.
  
          merge : bool
              Whether or not to merge child features together before summing
              them.
  
          ignore_strand : bool
              If True, then overlapping features on different strands will be
              merged together; otherwise, merging features with different strands
              will result in a ValueError.
  
          Returns
          -------
          Integer representing the total number of bp.