DictCache

• full name: tenpy.tools.cache.DictCache

• parent module: tenpy.tools.cache

• type: class

Inheritance Diagram

Methods

DictCache.__init__(storage)
DictCache.clear()
DictCache.create_subcache(name)	Create another DictCache based on the same storage resource.
DictCache.get(key[, default])	Same as self[key], but return default if key is not in self.
DictCache.items()
DictCache.keys()
DictCache.pop(k[,d])	If key is not found, d is returned if given, otherwise KeyError is raised.
DictCache.popitem()	as a 2-tuple; but raise KeyError if D is empty.
DictCache.preload(*keys[, raise_missing])	Pre-load the data for one or more keys from disk to RAM.
DictCache.set_short_term_keys(*keys)	Set keys for data which should be kept in RAM for a while.
DictCache.setdefault(k[,d])
DictCache.trivial()	Create a trivial storage that keeps everything in RAM.
DictCache.update([E, ]**F)	If E present and has a .keys() method, does: for k in E: D[k] = E[k] If E present and lacks .keys() method, does: for (k, v) in E: D[k] = v In either case, this is followed by: for k, v in F.items(): D[k] = v
DictCache.values()

class tenpy.tools.cache.DictCache(storage)

Bases: MutableMapping

Cache with dict-like interface.

The idea of the Cache is to save data that isn’t needed for a while in a long-term Storage container in order to free RAM. While the default Storage is just an interface around a plain dictionary and hence actually does keep everything in RAM, this class is designed to handle also the case of other storage classes like the PickleCache or Hdf5Cache. To avoid unnecessary read-write cycles, it keeps some values in a “short-term” cache in memory, see set_short_term_keys().

Using the preload() method allows to generalize to the ThreadedDictCache, which can save/load data in parallel without blocking the main thread execution while waiting for disk input/output.

Note

To allow a proper closing of opened storage, it is highly recommended to use the DictCache as a context manager in a with statement, see open().

Parameters:

storage (Storage) – Container for saving the data long-term.

long_term_storage

The storage passed during initialization.

Type:

Storage

long_term_keys

Keys of long_term_storage for which we have data.

Type:

set

short_term_cache

Dictionary for keeping a “short-term” memory of the keys in short_term_keys.

Type:

dict

short_term_keys

Keys for which data should be kept in short_term_cache.

Type:

set

Examples

The DictCache has as dict-like interface accepting strings as keys. The keys should be acceptable as filenames and not contain “/”.

>>> cache = DictCache.trivial()
>>> cache['a'] = 1
>>> cache['b'] = 2
>>> assert cache['a'] == 1
>>> assert cache.get('b') == 2
>>> "b" in cache
True
>>> "c" in cache
False
>>> assert cache.get('c', default=None) is None

classmethod trivial()

Create a trivial storage that keeps everything in RAM.

create_subcache(name)

Create another DictCache based on the same storage resource.

Uses Storage.subcontainer() to create another storage container for a new DictCache. The data is still completely owned by the top-most Storage (in turn owned by the CacheFile). Hence, closing the parent CacheFile will close all DictCache instances generated with create_subcache; accessing the data is no longer possible afterwards.

Parameters:

name (str) – Name of a subdirectory for the PickleCache or of a hdf5 subgroup for the Hdf5Cache.

Returns:

cache – Another class instance of the same type as self.

Return type:

DictCache

get(key, default=None)

Same as self[key], but return default if key is not in self.

set_short_term_keys(*keys)

Set keys for data which should be kept in RAM for a while.

Disk input/output is slow, so we want to avoid unnecessary read/write cycles. This method allows to specify keys the data of which should be kept in RAM after setting/ reading, until the keys are updated with the next call to set_short_term_keys(). The data is still written to disk in each self[key] = data, but (subsequent) reading data = self[key] will be fast for the given keys.

Parameters:

*keys (str) – The keys for which data should be kept in RAM for quick short-term lookup.

preload(*keys, raise_missing=False)

Pre-load the data for one or more keys from disk to RAM.

Parameters:

• *keys (str) – The keys which should be pre-loaded. Are added to the short_term_keys.

• raise_missing (bool) – Whether to raise a KeyError if a given key does not exist in self.

clear() → None.  Remove all items from D.

items() → a set-like object providing a view on D's items

keys() → a set-like object providing a view on D's keys

pop(k[, d]) → v, remove specified key and return the corresponding value.

If key is not found, d is returned if given, otherwise KeyError is raised.

popitem() → (k, v), remove and return some (key, value) pair

as a 2-tuple; but raise KeyError if D is empty.

setdefault(k[, d]) → D.get(k,d), also set D[k]=d if k not in D

update([E, ]**F) → None.  Update D from mapping/iterable E and F.

If E present and has a .keys() method, does: for k in E: D[k] = E[k] If E present and lacks .keys() method, does: for (k, v) in E: D[k] = v In either case, this is followed by: for k, v in F.items(): D[k] = v

values() → an object providing a view on D's values