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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 file(ctx, data_dir, data_file):
 """Use the File SWAG Backend"""

    if not ctx.file:
        ctx.data_file = data_file

    if not ctx.data_dir:
        ctx.data_dir = data_dir

    ctx.type = 'file'