input: def feature_extraction(input_str: str) -> dict:
      """ Extract features from a JSON string. The function should parse the JSON string,
      extract the 'id' and 'title' fields, and calculate the length of the 'body' field.
      Return these values in a dictionary.
      >>> feature_extraction('{"id": 111, "title": "This is a sample title", "body": "This is a sample body text"}')
      {'id': 111, 'title': 'This is a sample title', 'body_len': 29}
      """
output:     import json
      data = json.loads(input_str)
      return {
          'id': data['id'],
          'title': data['title'],
          'body_len': len(data['body'])
      }