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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 get_model(model, ctx, opt):
 """Model initialization."""

    kwargs = {'ctx': ctx, 'pretrained': opt.use_pretrained, 'classes': classes}
    if model.startswith('resnet'):
        kwargs['thumbnail'] = opt.use_thumbnail
    elif model.startswith('vgg'):
        kwargs['batch_norm'] = opt.batch_norm

    net = models.get_model(model, **kwargs)
    if opt.resume:
        net.load_parameters(opt.resume)
    elif not opt.use_pretrained:
        if model in ['alexnet']:
            net.initialize(mx.init.Normal())
        else:
            net.initialize(mx.init.Xavier(magnitude=2))
    net.cast(opt.dtype)
    return net