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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 get_aligner_with_aliases(aligner, data):
 """Retrieve aligner index retriever, including aliases for shared. Handles tricky cases like gridss where we need bwa indices even with no aligner specified since they're used internally within GRIDSS. """

    aligner_aliases = {"sentieon-bwa": "bwa"}
    from bcbio import structural
    if not aligner and "gridss" in structural.get_svcallers(data):
        aligner = "bwa"
    return aligner_aliases.get(aligner) or aligner