<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _add_batch(x, sample):
 """Potentially add batch name to an upload file. """

    added = False
    for batch in sorted(dd.get_batches(sample) or [], key=len, reverse=True):
        if batch and os.path.basename(x["path"]).startswith(("%s-" % batch, "%s.vcf" % batch)):
            x["batch"] = batch
            added = True
            break
    if not added:
        x["batch"] = dd.get_sample_name(sample)
    return x