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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _diff(old_pipeline_definition, new_pipeline_definition):
    '''
    Return string diff of pipeline definitions.
    '''
    old_pipeline_definition.pop('ResponseMetadata', None)
    new_pipeline_definition.pop('ResponseMetadata', None)

    diff = salt.utils.data.decode(difflib.unified_diff(
        salt.utils.json.dumps(old_pipeline_definition, indent=4).splitlines(True),
        salt.utils.json.dumps(new_pipeline_definition, indent=4).splitlines(True),
    ))
    return ''.join(diff)