py-12-txn-kvstore
0.750
Challenge · difficulty 5/5
# Transactional key-value store
Implement a file **`solution.py`** containing a class `KVStore` that behaves like an in-memory
key-value map with **nested transactions**.
```python
class KVStore:
def __init__(self): ...
def get(self, key): ... # current value, or None if absent
def set(self, key, value): ...
def delete(self, key): ... # remove key (no-op if absent)
def keys(self): ... # sorted list of currently-visible keys
def __len__(self): ... # number of currently-visible keys
def begin(self): ... # open a new (nested) transaction
def commit(self): ... # merge the innermost open transaction into its parent
def rollback(self): ... # discard the innermost open transaction
```
## Semantics
- With **no open transaction**, `set`/`delete` mutate the committed store directly.
- `begin()` opens a transaction. Transactions **nest**: a second `begin()` opens a child of the
first. All `set`/`delete` calls apply to the **innermost** open transaction only.
- `get`, `keys`, and `__len__` always reflect the **currently-visible** state: the committed store
overlaid by every open transaction in order (innermost wins). A key `delete`d in an open
transaction is invisible even if it exists in the committed store.
- `commit()` merges the innermost transaction's changes (both sets and deletes) into its parent
(the enclosing transaction, or the committed store if it was the outermost). The transaction is
then closed.
- `rollback()` discards the innermost transaction's changes entirely and closes it.
- `commit()` or `rollback()` with **no open transaction** must raise `RuntimeError`.
- `keys()` returns the visible keys in **sorted order**.
## Example
```python
s = KVStore()
s.set("a", 1)
s.begin()
s.set("a", 2)
s.set("b", 3)
assert s.get("a") == 2 # innermost transaction wins
s.begin()
s.delete("a")
assert s.get("a") is None # deleted in the inner transaction
assert s.get("b") == 3 # still visible from the outer transaction
s.rollback() # discard the inner transaction
assert s.get("a") == 2 # back to the outer transaction's value
s.commit() # merge outer transaction into the committed store
assert s.get("a") == 2 and s.get("b") == 3
assert s.keys() == ["a", "b"]
```
tests/test_kvstore.py
import pytest
from solution import KVStore
def test_basic_set_get_delete():
s = KVStore()
assert s.get("a") is None
s.set("a", 1)
s.set("b", 2)
assert s.get("a") == 1
assert s.get("b") == 2
s.delete("a")
assert s.get("a") is None
s.delete("missing") # no-op, must not raise
def test_len_and_keys_sorted():
s = KVStore()
s.set("z", 1)
s.set("a", 1)
s.set("m", 1)
assert s.keys() == ["a", "m", "z"]
assert len(s) == 3
s.delete("m")
assert s.keys() == ["a", "z"]
assert len(s) == 2
def test_transaction_isolation_then_commit():
s = KVStore()
s.set("a", 1)
s.begin()
s.set("a", 2)
s.set("b", 3)
assert s.get("a") == 2
assert s.get("b") == 3
s.commit()
assert s.get("a") == 2
assert s.get("b") == 3
def test_rollback_discards_changes():
s = KVStore()
s.set("a", 1)
s.begin()
s.set("a", 99)
s.set("b", 5)
s.rollback()
assert s.get("a") == 1
assert s.get("b") is None
assert s.keys() == ["a"]
def test_delete_within_transaction_is_isolated():
s = KVStore()
s.set("a", 1)
s.begin()
s.delete("a")
assert s.get("a") is None
assert s.keys() == []
assert len(s) == 0
s.rollback()
assert s.get("a") == 1 # delete was rolled back
def test_commit_propagates_delete_to_committed_store():
s = KVStore()
s.set("a", 1)
s.begin()
s.delete("a")
s.commit()
assert s.get("a") is None
assert s.keys() == []
def test_nested_transactions_inner_rollback():
s = KVStore()
s.set("a", 1)
s.begin()
s.set("a", 2)
s.set("b", 3)
s.begin()
s.delete("a")
assert s.get("a") is None
assert s.get("b") == 3
s.rollback() # discard inner
assert s.get("a") == 2 # outer value restored
s.commit() # merge outer into committed
assert s.get("a") == 2
assert s.get("b") == 3
def test_nested_commit_merges_into_parent_not_base():
s = KVStore()
s.begin()
s.set("a", 1)
s.begin()
s.set("a", 2)
s.set("b", 3)
s.commit() # inner -> outer (NOT committed store yet)
assert s.get("a") == 2
assert s.get("b") == 3
s.rollback() # discard outer -> everything gone
assert s.get("a") is None
assert s.get("b") is None
assert len(s) == 0
def test_commit_without_transaction_raises():
s = KVStore()
with pytest.raises(RuntimeError):
s.commit()
def test_rollback_without_transaction_raises():
s = KVStore()
with pytest.raises(RuntimeError):
s.rollback()
def test_deep_nesting_visibility_and_merge():
s = KVStore()
s.set("k", 0)
for depth in range(1, 6):
s.begin()
s.set("k", depth)
assert s.get("k") == depth
# commit all five layers down to the base
for _ in range(5):
s.commit()
assert s.get("k") == 5
assert s.keys() == ["k"]
def test_reset_value_after_delete_in_same_transaction():
s = KVStore()
s.set("a", 1)
s.begin()
s.delete("a")
s.set("a", 7) # re-add after delete within the same transaction
assert s.get("a") == 7
s.commit()
assert s.get("a") == 7
System prompt
You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.Proposed solution
```python
class KVStore:
def __init__(self):
self._committed = {}
self._transactions = []
def get(self, key):
# Check from innermost to outermost transactions
for tx in reversed(self._transactions):
if key in tx:
return tx[key]
if key in tx.get('_deleted', set()):
return None
return self._committed.get(key)
def set(self, key, value):
if not self._transactions:
self._committed[key] = value
else:
tx = self._transactions[-1]
tx[key] = value
if key in tx.get('_deleted', set()):
del tx['_deleted'][key]
def delete(self, key):
if not self._transactions:
if key in self._committed:
del self._committed[key]
else:
tx = self._transactions[-1]
if key in tx:
del tx[key]
else:
tx.setdefault('_deleted', set()).add(key)
def keys(self):
visible = set(self._committed.keys())
for tx in self._transactions:
visible.update(tx.keys())
visible.difference_update(tx.get('_deleted', set()))
return sorted(visible)
def __len__(self):
return len(self.keys())
def begin(self):
self._transactions.append({})
def commit(self):
if not self._transactions:
raise RuntimeError("No open transaction")
tx = self._transactions.pop()
if self._transactions:
parent = self._transactions[-1]
for key, value in tx.items():
parent[key] = value
if key in parent.get('_deleted', set()):
del parent['_deleted'][key]
for key in tx.get('_deleted', set()):
parent.setdefault('_deleted', set()).add(key)
else:
self._committed.update(tx)
for key in tx.get('_deleted', set()):
if key in self._committed:
del self._committed[key]
def rollback(self):
if not self._transactions:
raise RuntimeError("No open transaction")
self._transactions.pop()
```Test output (stdout)
....FF.....F [100%]
=================================== FAILURES ===================================
__________________ test_delete_within_transaction_is_isolated __________________
def test_delete_within_transaction_is_isolated():
s = KVStore()
s.set("a", 1)
s.begin()
s.delete("a")
assert s.get("a") is None
> assert s.keys() == []
E AssertionError: assert ['_deleted'] == []
E
E Left contains one more item: '_deleted'
E Use -v to get more diff
test_kvstore.py:61: AssertionError
_______________ test_commit_propagates_delete_to_committed_store _______________
def test_commit_propagates_delete_to_committed_store():
s = KVStore()
s.set("a", 1)
s.begin()
s.delete("a")
s.commit()
assert s.get("a") is None
> assert s.keys() == []
E AssertionError: assert ['_deleted'] == []
E
E Left contains one more item: '_deleted'
E Use -v to get more diff
test_kvstore.py:74: AssertionError
______________ test_reset_value_after_delete_in_same_transaction _______________
def test_reset_value_after_delete_in_same_transaction():
s = KVStore()
s.set("a", 1)
s.begin()
s.delete("a")
> s.set("a", 7) # re-add after delete within the same transaction
^^^^^^^^^^^^^
test_kvstore.py:141:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
self = <solution.KVStore object at 0x77bbaeec05c0>, key = 'a', value = 7
def set(self, key, value):
if not self._transactions:
self._committed[key] = value
else:
tx = self._transactions[-1]
tx[key] = value
if key in tx.get('_deleted', set()):
> del tx['_deleted'][key]
^^^^^^^^^^^^^^^^^^^
E TypeError: 'set' object does not support item deletion
solution.py:22: TypeError
=========================== short test summary info ============================
FAILED test_kvstore.py::test_delete_within_transaction_is_isolated - Assertio...
FAILED test_kvstore.py::test_commit_propagates_delete_to_committed_store - As...
FAILED test_kvstore.py::test_reset_value_after_delete_in_same_transaction - T...
3 failed, 9 passed in 0.03s
Self-repair attempts
[
{
"total": 12,
"answer": "```python\nclass KVStore:\n def __init__(self):\n self._committed = {}\n self._transactions = []\n\n def get(self, key):\n # Check from innermost to outermost transactions\n for tx in reversed(self._transactions):\n if key in tx:\n return tx[key]\n if key in tx.get('_deleted', set()):\n return None\n return self._committed.get(key)\n\n def set(self, key, value):\n if not self._transactions:\n self._committed[key] = value\n else:\n tx = self._transactions[-1]\n tx[key] = value\n if key in tx.get('_deleted', set()):\n del tx['_deleted'][key]\n\n def delete(self, key):\n if not self._transactions:\n if key in self._committed:\n del self._committed[key]\n else:\n tx = self._transactions[-1]\n if key in tx:\n del tx[key]\n else:\n tx.setdefault('_deleted', set()).add(key)\n\n def keys(self):\n visible = set(self._committed.keys())\n for tx in self._transactions:\n visible.update(tx.keys())\n visible.difference_update(tx.get('_deleted', set()))\n return sorted(visible)\n\n def __len__(self):\n return len(self.keys())\n\n def begin(self):\n self._transactions.append({})\n\n def commit(self):\n if not self._transactions:\n raise RuntimeError(\"No open transaction\")\n tx = self._transactions.pop()\n if self._transactions:\n parent = self._transactions[-1]\n for key, value in tx.items():\n parent[key] = value\n if key in parent.get('_deleted', set()):\n del parent['_deleted'][key]\n for key in tx.get('_deleted', set()):\n parent.setdefault('_deleted', set()).add(key)\n else:\n self._committed.update(tx)\n for key in tx.get('_deleted', set()):\n if key in self._committed:\n del self._committed[key]\n\n def rollback(self):\n if not self._transactions:\n raise RuntimeError(\"No open transaction\")\n self._transactions.pop()\n```",
"passed": 9,
"test_error": "....FF.....F [100%]\n=================================== FAILURES ===================================\n__________________ test_delete_within_transaction_is_isolated __________________\n\n def test_delete_within_transaction_is_isolated():\n s = KVStore()\n s.set(\"a\", 1)\n s.begin()\n s.delete(\"a\")\n assert s.get(\"a\") is None\n> assert s.keys() == []\nE AssertionError: assert ['_deleted'] == []\nE \nE Left contains one more item: '_deleted'\nE Use -v to get more diff\n\ntest_kvstore.py:61: AssertionError\n_______________ test_commit_propagates_delete_to_committed_store _______________\n\n def test_commit_propagates_delete_to_committed_store():\n s = KVStore()\n s.set(\"a\", 1)\n s.begin()\n s.delete(\"a\")\n s.commit()\n assert s.get(\"a\") is None\n> assert s.keys() == []\nE AssertionError: assert ['_deleted'] == []\nE \nE Left contains one more item: '_deleted'\nE Use -v to get more diff\n\ntest_kvstore.py:74: AssertionError\n______________ test_reset_value_after_delete_in_same_transaction _______________\n\n def test_reset_value_after_delete_in_same_transaction():\n s = KVStore()\n s.set(\"a\", 1)\n s.begin()\n s.delete(\"a\")\n> s.set(\"a\", 7) # re-add after delete within the same transaction\n ^^^^^^^^^^^^^\n\ntest_kvstore.py:141: \n_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ \n\nself = <solution.KVStore object at 0x77bbaeec05c0>, key = 'a', value = 7\n\n def set(self, key, value):\n if not self._transactions:\n self._committed[key] = value\n else:\n tx = self._transactions[-1]\n tx[key] = value\n if key in tx.get('_deleted', set()):\n> del tx['_deleted'][key]\n ^^^^^^^^^^^^^^^^^^^\nE TypeError: 'set' object does not support item deletion\n\nsolution.py:22: TypeError\n=========================== short test summary info ============================\nFAILED test_kvstore.py::test_delete_within_transaction_is_isolated - Assertio...\nFAILED test_kvstore.py::test_commit_propagates_delete_to_committed_store - As...\nFAILED test_kvstore.py::test_reset_value_after_delete_in_same_transaction - T...\n3 failed, 9 passed in 0.03s"
},
{
"total": 12,
"answer": "```python\nclass KVStore:\n def __init__(self):\n self._committed = {}\n self._transactions = []\n\n def get(self, key):\n # Check from innermost to outermost transactions\n for tx in reversed(self._transactions):\n if key in tx:\n return tx[key]\n if '_deleted' in tx and key in tx['_deleted']:\n return None\n return self._committed.get(key)\n\n def set(self, key, value):\n if not self._transactions:\n self._committed[key] = value\n else:\n tx = self._transactions[-1]\n tx[key] = value\n if '_deleted' in tx and key in tx['_deleted']:\n tx['_deleted'].remove(key)\n\n def delete(self, key):\n if not self._transactions:\n if key in self._committed:\n del self._committed[key]\n else:\n tx = self._transactions[-1]\n if key in tx:\n del tx[key]\n else:\n if '_deleted' not in tx:\n tx['_deleted'] = set()\n tx['_deleted'].add(key)\n\n def keys(self):\n visible = set(self._committed.keys())\n for tx in self._transactions:\n visible.update(tx.keys())\n if '_deleted' in tx:\n visible.difference_update(tx['_deleted'])\n return sorted(visible)\n\n def __len__(self):\n return len(self.keys())\n\n def begin(self):\n self._transactions.append({})\n\n def commit(self):\n if not self._transactions:\n raise RuntimeError(\"No open transaction\")\n tx = self._transactions.pop()\n if self._transactions:\n parent = self._transactions[-1]\n for key, value in tx.items():\n parent[key] = value\n if '_deleted' in parent and key in parent['_deleted']:\n parent['_deleted'].remove(key)\n if '_deleted' in tx:\n if '_deleted' not in parent:\n parent['_deleted'] = set()\n parent['_deleted'].update(tx['_deleted'])\n else:\n self._committed.update(tx)\n if '_deleted' in tx:\n for key in tx['_deleted']:\n if key in self._committed:\n del self._committed[key]\n\n def rollback(self):\n if not self._transactions:\n raise RuntimeError(\"No open transaction\")\n self._transactions.pop()\n```",
"passed": 10,
"test_error": "....FF...... [100%]\n=================================== FAILURES ===================================\n__________________ test_delete_within_transaction_is_isolated __________________\n\n def test_delete_within_transaction_is_isolated():\n s = KVStore()\n s.set(\"a\", 1)\n s.begin()\n s.delete(\"a\")\n assert s.get(\"a\") is None\n> assert s.keys() == []\nE AssertionError: assert ['_deleted'] == []\nE \nE Left contains one more item: '_deleted'\nE Use -v to get more diff\n\ntest_kvstore.py:61: AssertionError\n_______________ test_commit_propagates_delete_to_committed_store _______________\n\n def test_commit_propagates_delete_to_committed_store():\n s = KVStore()\n s.set(\"a\", 1)\n s.begin()\n s.delete(\"a\")\n s.commit()\n assert s.get(\"a\") is None\n> assert s.keys() == []\nE AssertionError: assert ['_deleted'] == []\nE \nE Left contains one more item: '_deleted'\nE Use -v to get more diff\n\ntest_kvstore.py:74: AssertionError\n=========================== short test summary info ============================\nFAILED test_kvstore.py::test_delete_within_transaction_is_isolated - Assertio...\nFAILED test_kvstore.py::test_commit_propagates_delete_to_committed_store - As...\n2 failed, 10 passed in 0.03s"
},
{
"total": 12,
"answer": "```python\nclass KVStore:\n def __init__(self):\n self._committed = {}\n self._transactions = []\n\n def get(self, key):\n # Check from innermost to outermost transactions\n for tx in reversed(self._transactions):\n if key in tx:\n return tx[key]\n if '_deleted' in tx and key in tx['_deleted']:\n return None\n return self._committed.get(key)\n\n def set(self, key, value):\n if not self._transactions:\n self._committed[key] = value\n else:\n tx = self._transactions[-1]\n tx[key] = value\n if '_deleted' in tx and key in tx['_deleted']:\n tx['_deleted'].remove(key)\n\n def delete(self, key):\n if not self._transactions:\n if key in self._committed:\n del self._committed[key]\n else:\n tx = self._transactions[-1]\n if key in tx:\n del tx[key]\n else:\n if '_deleted' not in tx:\n tx['_deleted'] = set()\n tx['_deleted'].add(key)\n\n def keys(self):\n visible = set(self._committed.keys())\n for tx in self._transactions:\n visible.update(tx.keys())\n if '_deleted' in tx:\n visible.difference_update(tx['_deleted'])\n # Remove internal _deleted keys from the result\n visible.discard('_deleted')\n return sorted(visible)\n\n def __len__(self):\n return len(self.keys())\n\n def begin(self):\n self._transactions.append({})\n\n def commit(self):\n if not self._transactions:\n raise RuntimeError(\"No open transaction\")\n tx = self._transactions.pop()\n if self._transactions:\n parent = self._transactions[-1]\n for key, value in tx.items():\n parent[key] = value\n if '_deleted' in parent and key in parent['_deleted']:\n parent['_deleted'].remove(key)\n if '_deleted' in tx:\n if '_deleted' not in parent:\n parent['_deleted'] = set()\n parent['_deleted'].update(tx['_deleted'])\n else:\n self._committed.update(tx)\n if '_deleted' in tx:\n for key in tx['_deleted']:\n if key in self._committed:\n del self._committed[key]\n\n def rollback(self):\n if not self._transactions:\n raise RuntimeError(\"No open transaction\")\n self._transactions.pop()\n```",
"passed": 12,
"test_error": ""
}
]