code: def kernel_signature(
      f: NativeFunction,
      backend_index: BackendIndex,
      *,
      prefix: str = "",
  ) -> Union["NativeSignature", "DispatcherSignature"]:
      # Note [External Backends Follow Dispatcher API]
      # Kernel signatures for in-tree backends follow the "native" API,
      # while kernels for out-of-tree backends follow the dispatcher API.
      # See the comments in `native.py` for details, but historically there have been
      # some small differences in schema convention between them and the Dispatcher API.
      # Any differences that require translating between the two will results in a runtime cost,
      # so we'd like to keep the differences as small as possible.
      # With external backends, we'd like to enforce that they write their kernels with schemas
      # that match the Dispatcher API directly, if they can.
      meta = backend_index.get_kernel(f)
      symint = meta is not None and meta.supports_symint()
      if symint:
          assert (
              f.func.has_symint()
          ), f"attempted to define symint kernel for {backend_index.dispatch_key} without SymInt in schema"
      if backend_index.external:
          return DispatcherSignature.from_schema(
              f.func, prefix=prefix, symint=symint
          )
      else:
          return NativeSignature(f.func, prefix=prefix, symint=symint)
  
imports: from dataclasses import dataclass
  from typing import Iterator, List, Optional, Sequence, Set, Tuple, Union
  from torchgen.model import BackendIndex, FunctionSchema, NativeFunction, NativeFunctionsGroup, NativeFunctionsViewGroup
  from .types_base import Binding, CType, Expr
  from torchgen.api import cpp, dispatcher, functionalization, native, structured, translate
label_desc: Use image node_id 1 for calling a global function with example usage: kernel_signature(f, backend_index) and returns: DispatcherSignature, NativeSignature