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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
from typing import Any, Union
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, items=None):
# type: (Union[int, None], Union[float, None], Union[None,dict,OrderedDict,ExpiringDict]) -> None
if not self.__is_instance_of_expiring_dict(items):
self.__assertions(max_len, max_age_seconds)
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
if items is not None:
if self.__is_instance_of_expiring_dict(items):
self.__copy_expiring_dict(max_len, max_age_seconds, items)
elif self.__is_instance_of_dict(items):
self.__copy_dict(items)
elif self.__is_reduced_result(items):
self.__copy_reduced_result(items)
else:
raise ValueError('can not unpack items')
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_time=None):
""" Set d[key] to value. """
with self.lock:
if len(self) == self.max_len:
if key in self:
del self[key]
else:
try:
self.popitem(last=False)
except KeyError:
pass
if set_time is None:
set_time = time.time()
OrderedDict.__setitem__(self, key, (value, set_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) # type: Any, Union[None, float]
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 items_with_timestamp(self):
""" Return a copy of the dictionary's list of (key, value, timestamp) triples. """
r = []
for key in self._safe_keys():
try:
r.append((key, OrderedDict.__getitem__(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()
def __reduce__(self):
reduced = self.__class__, (self.max_len, self.max_age, ('reduce_result', self.items_with_timestamp()))
return reduced
def __assertions(self, max_len, max_age_seconds):
self.__assert_max_len(max_len)
self.__assert_max_age_seconds(max_age_seconds)
@staticmethod
def __assert_max_len(max_len):
assert max_len >= 1
@staticmethod
def __assert_max_age_seconds(max_age_seconds):
assert max_age_seconds >= 0
@staticmethod
def __is_reduced_result(items):
if len(items) == 2 and items[0] == 'reduce_result':
return True
return False
@staticmethod
def __is_instance_of_expiring_dict(items):
if items is not None:
if isinstance(items, ExpiringDict):
return True
return False
@staticmethod
def __is_instance_of_dict(items):
if isinstance(items, dict):
return True
return False
def __copy_expiring_dict(self, max_len, max_age_seconds, items):
# type: (Union[int, None], Union[float, None], Any) -> None
if max_len is not None:
self.__assert_max_len(max_len)
self.max_len = max_len
else:
self.max_len = items.max_len
if max_age_seconds is not None:
self.__assert_max_age_seconds(max_age_seconds)
self.max_age = max_age_seconds
else:
self.max_age = items.max_age
[self.__setitem__(key, value, set_time) for key, (value, set_time) in items.items_with_timestamp()]
def __copy_dict(self, items):
# type: (dict) -> None
[self.__setitem__(key, value) for key, value in items.items()]
def __copy_reduced_result(self, items):
[self.__setitem__(key, value, set_time) for key, (value, set_time) in items[1]]
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