Source code for zict.buffer
from itertools import chain
from .common import ZictBase, close
from .lru import LRU
[docs]class Buffer(ZictBase):
""" Buffer one dictionary on top of another
This creates a MutableMapping by combining two MutableMappings, one that
feeds into the other when it overflows, based on an LRU mechanism. When
the first evicts elements these get placed into the second. When an item
is retrieved from the second it is placed back into the first.
Parameters
----------
fast: MutableMapping
slow: MutableMapping
fast_to_slow_callbacks: list of callables
These functions run every time data moves from the fast to the slow
mapping. They take two arguments, a key and a value
slow_to_fast_callbacks: list of callables
These functions run every time data moves form the slow to the fast
mapping.
Examples
--------
>>> fast = dict()
>>> slow = Func(dumps, loads, File('storage/')) # doctest: +SKIP
>>> def weight(k, v):
... return sys.getsizeof(v)
>>> buff = Buffer(fast, slow, 1e8, weight=weight) # doctest: +SKIP
See Also
--------
LRU
"""
def __init__(self, fast, slow, n, weight=lambda k, v: 1,
fast_to_slow_callbacks=None, slow_to_fast_callbacks=None):
self.fast = LRU(n, fast, weight=weight, on_evict=[self.fast_to_slow])
self.slow = slow
self.n = n
self.weight = weight
if callable(fast_to_slow_callbacks):
fast_to_slow_callbacks = [fast_to_slow_callbacks]
if callable(slow_to_fast_callbacks):
slow_to_fast_callbacks = [slow_to_fast_callbacks]
self.fast_to_slow_callbacks = fast_to_slow_callbacks or []
self.slow_to_fast_callbacks = slow_to_fast_callbacks or []
def fast_to_slow(self, key, value):
self.slow[key] = value
for cb in self.fast_to_slow_callbacks:
cb(key, value)
def slow_to_fast(self, key):
value = self.slow[key]
# Avoid useless movement for heavy values
if self.weight(key, value) <= self.n:
del self.slow[key]
self.fast[key] = value
for cb in self.slow_to_fast_callbacks:
cb(key, value)
return value
def __getitem__(self, key):
if key in self.fast:
return self.fast[key]
elif key in self.slow:
return self.slow_to_fast(key)
else:
raise KeyError(key)
def __setitem__(self, key, value):
weight = self.weight(key, value)
# Avoid useless movement for heavy values
if self.weight(key, value) <= self.n:
if key in self.slow:
del self.slow[key]
self.fast[key] = value
else:
self.slow[key] = value
def __delitem__(self, key):
if key in self.fast:
del self.fast[key]
elif key in self.slow:
del self.slow[key]
else:
raise KeyError(key)
[docs] def keys(self):
return chain(self.fast.keys(), self.slow.keys())
[docs] def values(self):
return chain(self.fast.values(), self.slow.values())
[docs] def items(self):
return chain(self.fast.items(), self.slow.items())
def __len__(self):
return len(self.fast) + len(self.slow)
def __iter__(self):
return chain(iter(self.fast), iter(self.slow))
def __contains__(self, key):
return key in self.fast or key in self.slow
def __str__(self):
return 'Buffer<%s, %s>' % (str(self.fast), str(self.slow))
__repr__ = __str__
def flush(self):
self.fast.flush()
self.slow.flush()
[docs] def close(self):
close(self.fast)
close(self.slow)