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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 _datatarget_defaults(args, default_args):
 """Set data installation targets, handling defaults. Sets variation, rnaseq, smallrna as default targets if we're not isolated to a single method. Provides back compatibility for toolplus specifications. """

    default_data = default_args.get("datatarget", [])
    # back-compatible toolplus specifications
    for x in default_args.get("toolplus", []):
        val = None
        if x == "data":
            val = "gemini"
        elif x in ["cadd", "dbnsfp", "dbscsnv", "kraken", "gnomad"]:
            val = x
        if val and val not in default_data:
            default_data.append(val)
    new_val = getattr(args, "datatarget")
    for x in default_data:
        if x not in new_val:
            new_val.append(x)
    has_std_target = False
    std_targets = ["variation", "rnaseq", "smallrna"]
    for target in std_targets:
        if target in new_val:
            has_std_target = True
            break
    if not has_std_target:
        new_val = new_val + std_targets
    setattr(args, "datatarget", new_val)
    return args