docstr: tensor 的 saclar 值
  
  :param tensor:
  :return:
docstr_tok: ["tensor","\u7684","saclar","\u503c",":","param","tensor",":",":","return",":"]
code: def get_scalar(self, tensor) -> float:
      """
      tensor 的 saclar 值
  
      :param tensor:
      :return:
      """
      return tensor.item()
  
file_path: fastNLP/fastNLP/core/metrics/backend/jittor_backend/backend.py
imports: import numpy
  from fastNLP.envs.imports import _NEED_IMPORT_JITTOR
  from fastNLP.core.metrics.backend import Backend
label_desc: Use image node_id 5 for calling the JittorBackend obj's underlying member method code with example usage: obj.get_scalar(tensor) and returns: tensor