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'''
Dictionary with auto-expiring values for caching purposes.
Expiration happens on any access, object is locked during cleanup from expired
values. Can not store more than max_len elements - the oldest will be deleted.
>>> ExpiringDict(max_len=100, max_age_seconds=10)
The values stored in the following way:
{
key1: (value1, created_time1),
key2: (value2, created_time2)
}
NOTE: iteration over dict and also keys() do not remove expired values!
'''
import time
from threading import RLock
import sys
try:
from collections import OrderedDict
except ImportError:
# Python < 2.7
from ordereddict import OrderedDict
class ExpiringDict(OrderedDict):
def __init__(self, max_len, max_age_seconds):
assert max_age_seconds >= 0
assert max_len >= 1
OrderedDict.__init__(self)
self.max_len = max_len
self.max_age = max_age_seconds
self.lock = RLock()
if sys.version_info >= (3, 5):
self._safe_keys = lambda: list(self.keys())
else:
self._safe_keys = self.keys
def __contains__(self, key):
""" Return True if the dict has a key, else return False. """
try:
with self.lock:
item = OrderedDict.__getitem__(self, key)
if time.time() - item[1] < self.max_age:
return True
else:
del self[key]
except KeyError:
pass
return False
def __getitem__(self, key, with_age=False):
""" Return the item of the dict.
Raises a KeyError if key is not in the map.
"""
with self.lock:
item = OrderedDict.__getitem__(self, key)
item_age = time.time() - item[1]
if item_age < self.max_age:
if with_age:
return item[0], item_age
else:
return item[0]
else:
del self[key]
raise KeyError(key)
def __setitem__(self, key, value):
""" Set d[key] to value. """
with self.lock:
if len(self) == self.max_len:
try:
self.popitem(last=False)
except KeyError:
pass
OrderedDict.__setitem__(self, key, (value, time.time()))
def pop(self, key, default=None):
""" Get item from the dict and remove it.
Return default if expired or does not exist. Never raise KeyError.
"""
with self.lock:
try:
item = OrderedDict.__getitem__(self, key)
del self[key]
return item[0]
except KeyError:
return default
def ttl(self, key):
""" Return TTL of the `key` (in seconds).
Returns None for non-existent or expired keys.
"""
key_value, key_age = self.get(key, with_age=True)
if key_age:
key_ttl = self.max_age - key_age
if key_ttl > 0:
return key_ttl
return None
def get(self, key, default=None, with_age=False):
" Return the value for key if key is in the dictionary, else default. "
try:
return self.__getitem__(key, with_age)
except KeyError:
if with_age:
return default, None
else:
return default
def items(self):
""" Return a copy of the dictionary's list of (key, value) pairs. """
r = []
for key in self._safe_keys():
try:
r.append((key, self[key]))
except KeyError:
pass
return r
def values(self):
""" Return a copy of the dictionary's list of values.
See the note for dict.items(). """
r = []
for key in self._safe_keys():
try:
r.append(self[key])
except KeyError:
pass
return r
def fromkeys(self):
" Create a new dictionary with keys from seq and values set to value. "
raise NotImplementedError()
def iteritems(self):
""" Return an iterator over the dictionary's (key, value) pairs. """
raise NotImplementedError()
def itervalues(self):
""" Return an iterator over the dictionary's values. """
raise NotImplementedError()
def viewitems(self):
" Return a new view of the dictionary's items ((key, value) pairs). "
raise NotImplementedError()
def viewkeys(self):
""" Return a new view of the dictionary's keys. """
raise NotImplementedError()
def viewvalues(self):
""" Return a new view of the dictionary's values. """
raise NotImplementedError()
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