class_docstr: The wrapper of activations.
  
  Args:
      act (str, optional): The activation name in lowercase. It must be one of ['elu', 'gelu',
          'hardshrink', 'tanh', 'hardtanh', 'prelu', 'relu', 'relu6', 'selu', 'leakyrelu', 'sigmoid',
          'softmax', 'softplus', 'softshrink', 'softsign', 'tanhshrink', 'logsigmoid', 'logsoftmax',
          'hsigmoid']. Default: None, means identical transformation.
  
  Returns:
      A callable object of Activation.
  
  Raises:
      KeyError: When parameter `act` is not in the optional range.
  
  Examples:
  
      from paddleseg.models.common.activation import Activation
  
      relu = Activation("relu")
      print(relu)
      # <class 'paddle.nn.layer.activation.ReLU'>
  
      sigmoid = Activation("sigmoid")
      print(sigmoid)
      # <class 'paddle.nn.layer.activation.Sigmoid'>
  
      not_exit_one = Activation("not_exit_one")
      # KeyError: "not_exit_one does not exist in the current dict_keys(['elu', 'gelu', 'hardshrink',
      # 'tanh', 'hardtanh', 'prelu', 'relu', 'relu6', 'selu', 'leakyrelu', 'sigmoid', 'softmax',
      # 'softplus', 'softshrink', 'softsign', 'tanhshrink', 'logsigmoid', 'logsoftmax', 'hsigmoid'])"
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code: def forward(self, x):
      if self._act is not None:
          return self.act_func(x)
      else:
          return x
  
imports: import paddle.nn
label_desc: Use image node_id 2 for calling the Activation obj's underlying member method code with example usage: obj.forward(x) and returns: self, x