code: def test_dtypes_hashable() -> None:
      # ensure that all the types can be hashed, and that their hashes
      # are sufficient to ensure distinct entries in a dictionary/set
  
      all_dtypes = [
          getattr(datatypes, d)
          for d in dir(datatypes)
          if isinstance(getattr(datatypes, d), datatypes.DataType)
      ]
      assert len(set(all_dtypes + all_dtypes)) == len(all_dtypes)
      assert (
          len({pl.Datetime("ms"), pl.Datetime("us"), pl.Datetime("ns")})
          == 3
      )
      assert (
          len(
              {
                  pl.List,
                  pl.List(pl.Int16),
                  pl.List(pl.Int32),
                  pl.List(pl.Int64),
              }
          )
          == 4
      )
  
file_path: polars/py-polars/tests/unit/test_datatypes.py
imports: from __future__ import annotations
  import pickle
  from datetime import datetime, timedelta
  from typing import TYPE_CHECKING
  import pytest
  import polars
  from polars import datatypes
  from polars.datatypes import DTYPE_TEMPORAL_UNITS, DataTypeGroup, Field, Int64, List, Struct, py_type_to_dtype
label_desc: Use image node_id 9 for calling a global function with example usage: test_dtypes_hashable() without return types