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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 flatten_probas(probas, labels, ignore=None):
 """ Flattens predictions in the batch """

    B, C, H, W = probas.size()
    probas = probas.permute(0, 2, 3, 1).contiguous().view(-1, C)  # B * H * W, C = P, C
    labels = labels.view(-1)
    if ignore is None:
        return probas, labels
    valid = (labels != ignore)
    vprobas = probas[valid.nonzero().squeeze()]
    vlabels = labels[valid]
    return vprobas, vlabels