def mlp(sizes, activation, output_activation=nn.Identity):
    """
    Build a multi-layer perceptron in PyTorch.

    Args:
        sizes: Tuple, list, or other iterable giving the number of units
            for each layer of the MLP. 

        activation: Activation function for all layers except last.

        output_activation: Activation function for last layer.

    Returns:
        A PyTorch module that can be called to give the output of the MLP.
        (Use an nn.Sequential module.)

    """
    #######################
    #                     #
    #   YOUR CODE HERE    #
    #                     #
    #######################
    pass

    Build a multi-layer perceptron in PyTorch.

    Args:
        sizes: Tuple, list, or other iterable giving the number of units
            for each layer of the MLP. 

        activation: Activation function for all layers except last.

        output_activation: Activation function for last layer.

    Returns:
        A PyTorch module that can be called to give the output of the MLP.
        (Use an nn.Sequential module.)

    
spinup/exercises/pytorch/problem_set_1/exercise1_2.py