<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def create_dataset_file(root_dir, data):
 """Create a new dataset from a template."""

  file_path = os.path.join(root_dir, '{dataset_type}', '{dataset_name}.py')
  context = (
      _HEADER + _DATASET_DEFAULT_IMPORTS + _CITATION
      + _DESCRIPTION + _DATASET_DEFAULTS
  )

  with gfile.GFile(file_path.format(**data), 'w') as f:
    f.write(context.format(**data))