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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 up_by_files(to_sync, remote_dir=DEFAULT_REMOTE_DIR, remote_files=None):
 """Sync a given list of local files to `remote_dir` dir"""

    if remote_files is None:
        remote_files = command.map_files_raw(remote_dir=remote_dir)
    for local_file in to_sync:
        _sync_local_file(local_file, remote_dir, remote_files)