class_docstr: The implementation of InternalWindowProcessFunction for MergingWindowAssigner.
class_docstr_tok: ["The","implementation","of","InternalWindowProcessFunction","for","MergingWindowAssigner","."]
code: def _initialize_cache(self, key):
      tuple_key = tuple(key)
      self._sorted_windows = self._cached_sorted_windows.get(tuple_key)
      if self._sorted_windows is None:
          self._sorted_windows = [k for k in self._window_mapping]
          self._sorted_windows.sort()
          self._cached_sorted_windows.put(
              tuple_key, self._sorted_windows
          )
  
imports: from abc import abstractmethod, ABC
  from typing import Generic, List, Iterable, Dict, Set
  from pyflink.common import Row
  from pyflink.common.constants import MAX_LONG_VALUE
  from pyflink.datastream.state import MapState
  from pyflink.fn_execution.table.window_assigner import WindowAssigner, PanedWindowAssigner, MergingWindowAssigner
  from pyflink.fn_execution.table.window_context import Context, K, W
label_desc: Use image node_id 7 for calling the MergingWindowProcessFunction obj's underlying member method code with example usage: obj._initialize_cache(key) without return types