code: def test_iterate_on_a_python_data_source():
      source = python.PythonDataSource(length=42, getitem=getitem)
      i = 0
      for i, j in enumerate(iter(source)):
          assert i == j
      assert i == 41
  
file_path: datasets/tensorflow_datasets/core/data_sources/python_test.py
imports: import pickle
  from unittest import mock
  from tensorflow_datasets.core.data_sources import python
  import tree
label_desc: Use image node_id 3 for calling a global function with example usage: test_iterate_on_a_python_data_source() without return types