code: def __length_hint__(self):
      with self._mem.read_transaction:
          node = self._root_node
          if isinstance(node, LonelyRootNode):
              # Assume that the lonely root node is half full
              return node.max_children // 2
          # Assume that there are no holes in pages
          last_page = self._mem.last_page
          # Assume that 70% of nodes in a tree carry values
          num_leaf_nodes = int(last_page * 0.70)
          # Assume that every leaf node is half full
          num_records_per_leaf_node = int(
              (node.max_children + node.min_children) / 2
          )
          return num_leaf_nodes * num_records_per_leaf_node
  
imports: from functools import partial
  from logging import getLogger
  from typing import Optional, Union, Iterator, Iterable
  from .None import utils
  from .const import TreeConf
  from .entry import Record, Reference, OpaqueData
  from .memory import FileMemory
  from .node import Node, LonelyRootNode, RootNode, InternalNode, LeafNode, OverflowNode
  from .serializer import Serializer, IntSerializer
label_desc: Use image node_id 13 for calling the BPlusTree obj's underlying member method code with example usage: obj.__length_hint__() and returns: unknown, unknown