<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _clean_streams(repo, mapped_streams):
 """Clean mapped standard streams."""

    for stream_name in ('stdout', 'stderr'):
        stream = mapped_streams.get(stream_name)
        if not stream:
            continue

        path = os.path.relpath(stream, start=repo.working_dir)
        if (path, 0) not in repo.index.entries:
            os.remove(stream)
        else:
            blob = repo.index.entries[(path, 0)].to_blob(repo)
            with open(path, 'wb') as fp:
                fp.write(blob.data_stream.read())