def __getitem__(self, txn_key):
assert type(txn_key) == tuple and len(txn_key) == <NUM_LIT:2><EOL>txn, key = txn_key<EOL>_key = struct.pack('<STR_LIT>', self._slot) + self._serialize_key(key)<EOL>_data = txn.get(_key)<EOL>if _data:<EOL><INDENT>if self._decompress:<EOL><INDENT>_data = self._decompress(_data)<EOL><DEDENT>return self._deserialize_value(_data)<EOL><DEDENT>else:<EOL><INDENT>return None<EOL><DEDENT>
:param txn_key:
:return: