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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 _set_optimizer_param(optimizer, param_group, param_name, value):
 """Set a parameter on an all or a specific parameter group of an optimizer instance. To select all param groups, use ``param_group='all'``. """

    if param_group == 'all':
        groups = optimizer.param_groups
    else:
        groups = [optimizer.param_groups[int(param_group)]]

    for group in groups:
        group[param_name] = value