code: def __repr__(self):
      s = self.__class__.__name__
      s += f"(gamma={self.gamma}, "
      s += f"alpha={self.alpha}, "
      s += f"reduction={self.reduction})"
      return s
  
imports: import torch
  import torch.nn
  from torch.autograd import Function
  from torch.autograd.function import once_differentiable
  from ..utils import ext_loader
label_desc: Use image node_id 3 for calling the SigmoidFocalLoss obj's underlying member method code with example usage: obj.__repr__() and returns: s