Generate code specific to the construction of the sklearn Pipeline for export_pipeline.

    Parameters
    ----------
    pipeline_tree: list
        List of operators in the current optimized pipeline

    Returns
    -------
    Source code for the sklearn pipeline

def generate_export_pipeline_code(pipeline_tree, operators):
    """Generate code specific to the construction of the sklearn Pipeline for export_pipeline.

    Parameters
    ----------
    pipeline_tree: list
        List of operators in the current optimized pipeline

    Returns
    -------
    Source code for the sklearn pipeline

    """
    steps = _process_operator(pipeline_tree, operators)
    # number of steps in a pipeline
    num_step = len(steps)
    if num_step > 1:
        pipeline_text = "make_pipeline(\n{STEPS}\n)".format(STEPS=_indent(",\n".join(steps), 4))
    # only one operator (root = True)
    else:
        pipeline_text = "{STEPS}".format(STEPS=_indent(",\n".join(steps), 0))

    return pipeline_text