code: def _each_iter(self, key: str) -> "DictStrAny":
      err_message = (
          f"Could not find '{key}' in matrix group '{self.name}'"
      )
      with reraise(KeyError, EntryNotFound(err_message)):
          value = self.normalized_iterable[key]
  
      temp_dict = {self.pair.key: key, self.pair.value: value}
      with self.context.set_temporarily(temp_dict, reserve=True):
          # optimization: item and key can be removed on __exit__() as they
          # are top-level values, and are not merged recursively.
          # This helps us avoid cloning context, which is slower
          # (increasing the size of the context might increase
          # the no. of items to be generated which means more cloning,
          # i.e. quadratic complexity).
          generated = self._generate_name(key)
          entry = EntryDefinition(
              self.resolver, self.context, generated, self.template
          )
          try:
              # optimization: skip checking for syntax errors on each matrix
              # generated stages. We do it once when accessing template.
              return entry.resolve_stage(skip_checks=True)
          except ContextError as exc:
              format_and_raise(
                  exc, f"stage '{generated}'", self.relpath
              )
  
imports: import logging
  import os
  from collections.abc import Mapping, Sequence
  from copy import deepcopy
  from itertools import product
  from typing import TYPE_CHECKING, Any, Dict, List, NamedTuple, Optional, Tuple, Type, Union
  from funcy import collecting, first, isa, join, reraise
  from dvc.exceptions import DvcException
  from dvc.log import logger
  from dvc.parsing.interpolate import ParseError
  from dvc.utils.objects import cached_property
  from .context import Context, ContextError, KeyNotInContext, MergeError, Node, VarsAlreadyLoaded
  from .interpolate import check_recursive_parse_errors, is_interpolated_string, recurse, to_str
label_desc: Use image node_id 12 for calling the MatrixDefinition obj's underlying member method code with example usage: obj._each_iter(key) and returns: entry