code: def forward(self, input, label, mask=None, weight=None, name=None):
      loss = F.binary_cross_entropy(
          input, label, reduction=self.reduction
      )
      return loss
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import numpy
  import paddle
  from paddle import nn
  import paddle.nn.functional
label_desc: Use image node_id 2 for calling the BCELoss obj's underlying member method code with example usage: obj.forward(input, label, mask, weight, name) and returns: loss