class_docstr: A map-to-arrays dict, with deterministic Reservoir Sampling.
  
  Store each reservoir bucket by key, and each bucket is a list sampling
  with reservoir algorithm.
docstr: Get items with tag "key"
  
  Args:
      key: Key to finding bucket in reservoir buckets.
  
  Returns:
      One bucket in reservoir buckets by key.
docstr_tok: ["Get","items","with","tag","``","key","''","Args",":","key",":","Key","to","finding","bucket","in","reservoir","buckets",".","Returns",":","One","bucket","in","reservoir","buckets","by","key","."]
code: def _get_items(self, key):
      """Get items with tag "key"
  
      Args:
          key: Key to finding bucket in reservoir buckets.
  
      Returns:
          One bucket in reservoir buckets by key.
      """
      keys = self.keys
      with self._mutex:
          if key not in keys:
              raise KeyError("Key %s not in buckets.keys()" % key)
          return self._buckets[key].items
  
imports: import collections
  import random
  import threading
label_desc: Use image node_id 7 for calling the Reservoir obj's underlying member method code with example usage: obj._get_items(key) and returns: self