class_docstr: Serve parameters for a single process.
class_docstr_tok: ["Serve","parameters","for","a","single","process","."]
code: def grad_keys(self) -> Tuple[KeyT, ...]:
      return tuple(
          [key for key in self.param_keys if self.has_grad(*key)]
      )
  
file_path: thinc/thinc/backends/_param_server.py
imports: from typing import Any, Dict, Optional, Tuple
  from ..types import FloatsXd
  from ..util import get_array_module
label_desc: Use image node_id 3 for calling the ParamServer obj's underlying member method code with example usage: obj.grad_keys() and returns: tuple