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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 _prep_inputs(align_bams, ref_file, items):
 """Ensure inputs to calling are indexed as expected. """

    broad_runner = broad.runner_from_path("picard", items[0]["config"])
    broad_runner.run_fn("picard_index_ref", ref_file)
    for x in align_bams:
        bam.index(x, items[0]["config"])