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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 keras_dropout(layer, rate):
    '''keras dropout layer.
    '''

    from keras import layers

    input_dim = len(layer.input.shape)
    if input_dim == 2:
        return layers.SpatialDropout1D(rate)
    elif input_dim == 3:
        return layers.SpatialDropout2D(rate)
    elif input_dim == 4:
        return layers.SpatialDropout3D(rate)
    else:
        return layers.Dropout(rate)