<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def persist_as_png(structure_dict, filepath):
 """Saves pipeline diagram to disk as png file. Args: structure_dict (dict):
 dict returned by :func:`~steppy.base.Step.upstream_structure` filepath (str):
 filepath to which the png with pipeline visualization should be persisted """

    graph = _create_graph(structure_dict)
    graph.write(filepath, format='png')