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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 add_data_file(data_files, target, source):
 """Add an entry to data_files"""

    for t, f in data_files:
        if t == target:
            break
    else:
        data_files.append((target, []))
        f = data_files[-1][1]
    if source not in f:
        f.append(source)