code: def length_of_indexer(indexer, target=None) -> int:
      """
      Return the expected length of target[indexer]
  
      Returns
      -------
      int
      """
      if target is not None and isinstance(indexer, slice):
          target_len = len(target)
          start = indexer.start
          stop = indexer.stop
          step = indexer.step
          if start is None:
              start = 0
          elif start < 0:
              start += target_len
          if stop is None or stop > target_len:
              stop = target_len
          elif stop < 0:
              stop += target_len
          if step is None:
              step = 1
          elif step < 0:
              start, stop = stop + 1, start + 1
              step = -step
          return (stop - start + step - 1) // step
      elif isinstance(indexer, (ABCSeries, ABCIndex, np.ndarray, list)):
          if isinstance(indexer, list):
              indexer = np.array(indexer)
  
          if indexer.dtype == bool:
              # GH#25774
              return indexer.sum()
          return len(indexer)
      elif isinstance(indexer, range):
          return (indexer.stop - indexer.start) // indexer.step
      elif not is_list_like_indexer(indexer):
          return 1
      raise AssertionError("cannot find the length of the indexer")
  
file_path: pandas/pandas/core/indexers/utils.py
imports: from __future__ import annotations
  from typing import TYPE_CHECKING, Any
  import numpy
  from pandas._libs import lib
  from pandas.core.dtypes.common import is_array_like, is_bool_dtype, is_integer, is_integer_dtype, is_list_like
  from pandas.core.dtypes.dtypes import ExtensionDtype
  from pandas.core.dtypes.generic import ABCIndex, ABCSeries
label_desc: Use image node_id 8 for calling a global function with example usage: length_of_indexer(indexer, target) and returns: unknown, len, indexer, unknown, int