| 1 | import json |
| 2 | import os |
| 3 | |
| 4 | |
| 5 | class KV: |
| 6 | """See README.md; commits append one line to <path>.commits.""" |
| 7 | |
| 8 | def __init__(self, path): |
| 9 | self.path = path |
| 10 | self._staged = None |
| 11 | self._data = {} |
| 12 | if os.path.exists(path): |
| 13 | with open(path) as f: |
| 14 | self._data = json.load(f) |
| 15 | |
| 16 | def begin(self): |
| 17 | if self._staged is not None: |
| 18 | raise RuntimeError("transaction already open") |
| 19 | self._staged = {} |
| 20 | |
| 21 | def put(self, key, value): |
| 22 | if self._staged is None: |
| 23 | raise RuntimeError("put() outside a transaction; call begin() first") |
| 24 | self._staged[key] = value |
| 25 | |
| 26 | def commit(self): |
| 27 | if self._staged is None: |
| 28 | raise RuntimeError("no open transaction") |
| 29 | self._data.update(self._staged) |
| 30 | self._staged = None |
| 31 | tmp = self.path + ".tmp" |
| 32 | with open(tmp, "w") as f: |
| 33 | json.dump(self._data, f, sort_keys=True) |
| 34 | os.replace(tmp, self.path) |
| 35 | with open(self.path + ".commits", "a") as f: |
| 36 | f.write("commit\n") |
| 37 | |
| 38 | def get(self, key): |
| 39 | return self._data.get(key) |
| 40 |