code: def real_strides(
      self, ignore_valid=False
  ) -> Tuple[Optional[sint], ...]:
      if len(self.views) == 1 and self.views[-1].mask is None:
          return self.views[-1].strides
      idxs: List[Node] = [
          Variable(f"idx{i}", 0, s - 1)
          for i, s in enumerate(self.shape)
      ]
      idx, valid = self.expr_idxs(idxs)
      ret: List[Optional[sint]] = [None] * len(self.views[-1].shape)
      bad_idx_vars: Set[Variable] = set()
      for this_dim in idx.nodes if isinstance(idx, SumNode) else [idx]:
          idx_maybe, stride_maybe = (
              (this_dim.a, this_dim.b)
              if isinstance(this_dim, MulNode)
              else (this_dim, 1)
          )
          try:
              ret[idxs.index(idx_maybe)] = stride_maybe
          except ValueError:
              bad_idx_vars = bad_idx_vars.union(idx_maybe.vars())
      idx_vars, valid_vars = idx.vars(), valid.vars()
      for i, tidx in enumerate(idxs):
          if tidx in bad_idx_vars or (
              tidx in valid_vars and not ignore_valid
          ):
              ret[i] = None
          elif tidx not in idx_vars:
              ret[i] = 0
      return tuple(ret)
  
imports: from __future__ import annotations
  import functools, itertools, operator
  from dataclasses import dataclass
  from typing import Tuple, List, Optional, Dict, Set, cast, Union, Iterable
  from tinygrad.ops import MovementOps
  from tinygrad.helpers import prod, merge_dicts, getenv
  from tinygrad.shape.symbolic import Variable, MulNode, Node, SumNode, NumNode, sint
  from tinygrad.shape.view import View, _merge_dims
label_desc: Use image node_id 12 for calling the ShapeTracker obj's underlying member method code with example usage: obj.real_strides(ignore_valid) and returns: tuple, self