code: def insert(key, value):
      
      # Pickle the value.
      value = pickle.dumps(value, protocol=constants.PICKLE_PROTOCOL)
      # Store the value as binary data in a document.
      doc = {
          KEY_FIELD: key,
          VALUE_FIELD: Binary(value)
      }
      # Pickle and store the value with its key. If the key already exists, we
      # don't insert (since the key is a unique index), and we don't care.
      try:
          return collection.insert(doc)
      except pymongo.errors.DuplicateKeyError:
          return None
docs: Store a value with a key.
  
      If the key is already present in the database, this does nothing.