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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 source_file(pymux, variables):
 """ Source configuration file. """

    filename = os.path.expanduser(variables['<filename>'])
    try:
        with open(filename, 'rb') as f:
            for line in f:
                line = line.decode('utf-8')
                handle_command(pymux, line)
    except IOError as e:
        raise CommandException('IOError: %s' % (e, ))