In the last post I showed how to install the python LevelDB bindings. Here is how to wrap the python LevelDB API into a dict like API with the help of UserDict.DictMixin. In a subclass we will extend the the simple key<string>:value<string> mapping to a dict with arbitrary JSON serializablie values.
from UserDict import DictMixin import leveldb import json class LevelDict(DictMixin): """Dict Wrapper around the Google LevelDB Database""" def __init__(self, path): """Constructor for LevelDict""" self.path = path self.db = leveldb.LevelDB(self.path) def __getitem__(self, key): return self.db.Get(key) def __setitem__(self, key, value): self.db.Put(key, value) def __delitem__(self, key): self.db.Delete(key) def __iter__(self): for k, v in self.db.RangeIter(): yield v def keys(self): return [k for k, v in self.db.RangeIter()] def iteritems(self): return self.db.RangeIter() def rangescan(self, start=None, end=None): if start is None and end is None: return self.db.RangeIter() elif end is None: return self.db.RangeIter(start) else: return self.db.RangeIter(start, end)
To store more than just strings we will add JSON serialization to a subclass:
class LevelJsonDict(LevelDict): """Dict Wrapper around the Google LevelDB Database with JSON serialization""" def __getitem__(self, key): return json.loads(LevelDict.__getitem__(self, key)) def __setitem__(self, key, value): LevelDict.__setitem__(self, key, json.dumps(value)) def iteritems(self): for k, v in LevelDict.iteritems(self): yield k, json.loads(v) def rangescan(self, start=None, end=None): for k, v in LevelDict.rangescan(self, start, end): yield k, json.loads(v)
Now you have a fast JSON Store with a Dict based Interface and a LevelDB backend.