code: def calcavg_avgstrlen_subtrees(subtrees, dbg=False):
      
      ttl = 0
      for subtree in subtrees:
          ttl += subtree.avg_strlen
  
      crd = len(subtrees)
      avg = ttl/crd
      if dbg is True:
          print(avg)
      #       avg = ttl/crd
      return (avg, ttl, crd)
docs: In the effort of not using external libraries (like scipy, numpy, etc),
      I've written some harmless code for basic statistical calculations