from functools import lru_cache
import time
from collections.abc import MutableMapping
class DirCache(MutableMapping):
"""
Caching of directory listings, in a structure like
{"path0": [
{"name": "path0/file0",
"size": 123,
"type": "file",
...
},
{"name": "path0/file1",
},
...
],
"path1": [...]
}
Parameters to this class control listing expiry or indeed turn
caching off
"""
def __init__(
self,
use_listings_cache=True,
listings_expiry_time=None,
max_paths=None,
**kwargs
):
"""
Parameters
----------
use_listings_cache: bool
If False, this cache never returns items, but always reports KeyError,
and setting items has no effect
listings_expiry_time: int (optional)
Time in seconds that a listing is considered valid. If None,
listings do not expire.
max_paths: int (optional)
The number of most recent listings that are considered valid; 'recent'
refers to when the entry was set.
"""
self._cache = {}
self._times = {}
if max_paths:
self._q = lru_cache(max_paths + 1)(lambda key: self._cache.pop(key, None))
self.use_listings_cache = use_listings_cache
self.listings_expiry_time = listings_expiry_time
self.max_paths = max_paths
def __getitem__(self, item):
if self.listings_expiry_time:
if self._times.get(item, 0) - time.time() < -self.listings_expiry_time:
del self._cache[item]
if self.max_paths:
self._q(item)
return self._cache[item] # maybe raises KeyError
def clear(self):
self._cache.clear()
def __len__(self):
return len(self._cache)
def __contains__(self, item):
try:
self[item]
return True
except KeyError:
return False
def __setitem__(self, key, value):
if not self.use_listings_cache:
return
if self.max_paths:
self._q(key)
self._cache[key] = value
if self.listings_expiry_time:
self._times[key] = time.time()
def __delitem__(self, key):
del self._cache[key]
def __iter__(self):
return (k for k in self._cache if k in self)
def __reduce__(self):
return (
DirCache,
(self.use_listings_cache, self.listings_expiry_time, self.max_paths),
)
