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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 report_unknown(bytes_so_far, total_size, speed, eta):
    '''
    This callback for the download function is used
    when the total size is unknown
    '''
    sys.stdout.write(
        "Downloading: {0} / Unknown - {1}/s      ".format(approximate_size(bytes_so_far),
                                                          approximate_size(speed)))

    sys.stdout.write("\r")
    sys.stdout.flush()