code: def get_keys(self, engine):
      def get_bucket_keys(lshash):
          bucket = engine.storage.buckets[lshash.hash_name][
              lshash.hash_name
          ]
          return (i for v, i in bucket)
  
      return set(
          itertools.chain.from_iterable(
              get_bucket_keys(lshash) for lshash in engine.lshashes
          )
      )
  
imports: import itertools
  import unittest
  import numpy
  import scipy
  from future.builtins import range
  from nearpy import Engine
  from nearpy.utils.utils import unitvec
  from nearpy.hashes import UniBucket
label_desc: Use image node_id 2 for calling the TestDelete obj's underlying member method code with example usage: obj.get_keys(engine) and returns: set, unknown