code: def __init__(self, gamma=0, alpha=None, size_average=True):
      super(FocalLoss, self).__init__()
      self.gamma = gamma
      self.alpha = alpha
      if isinstance(alpha, (float, int)):
          self.alpha = torch.Tensor([alpha, 1 - alpha])
      if isinstance(alpha, list):
          self.alpha = torch.Tensor(alpha)
      self.size_average = size_average
  
imports: import torch
  import torch.nn
  import torch.nn.functional
  from torch.autograd import Variable
label_desc: Use image node_id 1 to create a new FocalLoss object from inherited base classes: nn with example: obj = FocalLoss(gamma, alpha, size_average)