class_docstr: Mapping from polars DataTypes to hypothesis Strategies.
  
  We customise this so that retrieval of nested strategies respects the inner dtype
  of List/Struct types; nested strategies are stored as callables that create the
  given strategy on demand (there are infinitely many possible nested dtypes).
class_docstr_tok: ["Mapping","from","polars","DataTypes","to","hypothesis","Strategies",".","We","customise","this","so","that","retrieval","of","nested","strategies","respects","the","inner","dtype","of","List\/Struct","types",";","nested","strategies","are","stored","as","callables","that","create","the","given","strategy","on","demand","(","there","are","infinitely","many","possible","nested","dtypes",")","."]
docstr: Return the number of items in the lookup.
docstr_tok: ["Return","the","number","of","items","in","the","lookup","."]
code: def __len__(self) -> int:
      """Return the number of items in the lookup."""
      return len(self._items)
  
imports: from __future__ import annotations
  import os
  from datetime import datetime, timedelta
  from itertools import chain
  from random import choice, shuffle
  from string import ascii_uppercase
  from typing import TYPE_CHECKING, Any, Callable, Iterator, Mapping, MutableMapping, Sequence
  from hypothesis.strategies import SearchStrategy, binary, booleans, characters, composite, dates, datetimes, decimals, floats, from_type, integers, lists, sampled_from, sets, text, timedeltas, times
  from polars.datatypes import Binary, Boolean, Categorical, Date, Datetime, Decimal, Duration, Float32, Float64, Int8, Int16, Int32, Int64, List, String, Time, UInt8, UInt16, UInt32, UInt64, is_polars_dtype
  from polars.type_aliases import PolarsDataType
  from polars.utils.deprecation import deprecate_nonkeyword_arguments
label_desc: Use image node_id 5 for calling the StrategyLookup obj's underlying member method code with example usage: obj.__len__() and returns: len