ubelt.util_cache module¶
This module exposes Cacher
and CacheStamp
classes, which
provide a simple API for on-disk caching.
The Cacher
class is the simplest and most direct method of caching. In
fact, it only requires four lines of boilderplate, which is the smallest
general and robust way that I (Jon Crall) have achieved, and I don’t think its
possible to do better. These four lines implement the following necessary and
sufficient steps for general robust on-disk caching.
Defining the cache dependenies
Checking if the cache missed
Loading the cache on a hit
Executing the process and saving the result on a miss.
The following example illustrates these four points.
Example
>>> import ubelt as ub
>>> # Define a cache name and dependencies (which is fed to `ub.hash_data`)
>>> cacher = ub.Cacher('name', depends='set-of-deps') # boilerplate:1
>>> # Calling tryload will return your data on a hit and None on a miss
>>> data = cacher.tryload(on_error='clear') # boilerplate:2
>>> # Check if you need to recompute your data
>>> if data is None: # boilerplate:3
>>> # Your code to recompute data goes here (this is not boilerplate).
>>> data = 'mydata'
>>> # Cache the computation result (via pickle)
>>> cacher.save(data) # boilerplate:4
Surprisingly this uses just as many boilerplate lines as a decorator style
cacher, but it is much more extensible. It is possible to use Cacher
in more sophisticated ways (e.g. metadata), but the simple in-line use is often
easier and cleaner. The following example illustrates this:
Example
>>> import ubelt as ub
>>> @ub.Cacher('name', depends={'dep1': 1, 'dep2': 2}) # boilerplate:1
>>> def func(): # boilerplate:2
>>> data = 'mydata'
>>> return data # boilerplate:3
>>> data = func() # boilerplate:4
>>> cacher = ub.Cacher('name', depends=['dependencies']) # boilerplate:1
>>> data = cacher.tryload(on_error='clear') # boilerplate:2
>>> if data is None: # boilerplate:3
>>> data = 'mydata'
>>> cacher.save(data) # boilerplate:4
While the above two are equivalent, the second version provides simpler tracebacks, explicit procedures, and makes it easier to use breakpoint debugging (because there is no closure scope).
While Cacher
is used to store direct results of in-line code in a
pickle format, the CacheStamp
object is used to cache processes that
produces an on-disk side effects other than the main return value. For
instance, consider the following example:
Example
>>> def compute_many_files(dpath):
... for i in range(0):
... fpath = '{}/file{}.txt'.format(dpath, i)
... open(fpath).write('foo' + str(i))
>>> #
>>> import ubelt as ub
>>> dpath = ub.ensure_app_cache_dir('ubelt/demo/cache')
>>> ub.delete(dpath) # start fresh
>>> # You must specify a directory, unlike in Cacher where it is optional
>>> self = ub.CacheStamp('name', dpath=dpath, depends={'a': 1, 'b': 2})
>>> if self.expired():
>>> compute_many_files(dpath)
>>> # Instead of caching the whole processes, we just write a file
>>> # that signals the process has been done.
>>> self.renew()
>>> assert not self.expired()
Todo
[ ] Remove the cfgstr-overrides?
- class ubelt.util_cache.Cacher(fname, depends=None, dpath=None, appname='ubelt', ext='.pkl', meta=None, verbose=None, enabled=True, log=None, hasher='sha1', protocol=- 1, cfgstr=None)[source]¶
Bases:
object
Cacher designed to be quickly integrated into existing scripts.
A dependency string can be specified, which will invalidate the cache if it changes to an unseen value. The location
- Parameters
fname (str) – A file name. This is the prefix that will be used by the cache. It will always be used as-is.
depends (str | List[str]) – Indicate dependencies of this cache. If the dependencies change, then the cache is recomputed. New in version 0.8.9, replaces cfgstr.
dpath (PathLike) – Specifies where to save the cache. If unspecified, Cacher defaults to an application resource dir as given by appname.
appname (str, default=’ubelt’) – Application name Specifies a folder in the application resource directory where to cache the data if
dpath
is not specified.ext (str, default=’.pkl’) – File extension for the cache format
meta (object) – Metadata that is also saved with the
cfgstr
. This can be useful to indicate how thecfgstr
was constructed.verbose (int, default=1) – Level of verbosity. Can be 1, 2 or 3.
enabled (bool, default=True) – If set to False, then the load and save methods will do nothing.
log (func) – Overloads the print function. Useful for sending output to loggers (e.g. logging.info, tqdm.tqdm.write, …)
hasher (str) – Type of hashing algorithm to use if
cfgstr
needs to be condensed to less than 49 characters.protocol (int, default=-1) – Protocol version used by pickle. Defaults to the -1 which is the latest protocol. If python 2 compatibility is not required, set to 2.
cfgstr (str) – Deprecated in favor of depends. Indicates the state. Either this string or a hash of this string will be used to identify the cache. A cfgstr should always be reasonably readable, thus it is good practice to hash extremely detailed cfgstrs to a reasonable readable level. Use meta to store make original details persist.
Example
>>> import ubelt as ub >>> depends = 'repr-of-params-that-uniquely-determine-the-process' >>> # Create a cacher and try loading the data >>> cacher = ub.Cacher('demo_process', depends, verbose=4) >>> cacher.clear() >>> data = cacher.tryload() >>> if data is None: >>> # Put expensive functions in if block when cacher misses >>> myvar1 = 'result of expensive process' >>> myvar2 = 'another result' >>> # Tell the cacher to write at the end of the if block >>> # It is idomatic to put results in an object named data >>> data = myvar1, myvar2 >>> cacher.save(data) >>> # Last part of the Cacher pattern is to unpack the data object >>> myvar1, myvar2 = data >>> # >>> # If we know the data exists, we can also simply call load >>> data = cacher.tryload()
Example
>>> # The previous example can be shorted if only a single value >>> from ubelt.util_cache import Cacher >>> depends = 'repr-of-params-that-uniquely-determine-the-process' >>> # Create a cacher and try loading the data >>> cacher = Cacher('demo_process', depends) >>> myvar = cacher.tryload() >>> if myvar is None: >>> myvar = ('result of expensive process', 'another result') >>> cacher.save(myvar) >>> assert cacher.exists(), 'should now exist'
- VERBOSE = 1¶
- FORCE_DISABLE = False¶
- get_fpath(cfgstr=None)[source]¶
Reports the filepath that the cacher will use.
It will attempt to use ‘{fname}_{cfgstr}{ext}’ unless that is too long. Then cfgstr will be hashed.
- Parameters
cfgstr (str, optional) – overrides the instance-level cfgstr
- Returns
PathLike
Example
>>> # xdoctest: +REQUIRES(module:pytest) >>> from ubelt.util_cache import Cacher >>> import pytest >>> with pytest.warns(UserWarning): >>> cacher = Cacher('test_cacher1') >>> cacher.get_fpath() >>> self = Cacher('test_cacher2', depends='cfg1') >>> self.get_fpath() >>> self = Cacher('test_cacher3', depends='cfg1' * 32) >>> self.get_fpath()
- exists(cfgstr=None)[source]¶
Check to see if the cache exists
- Parameters
cfgstr (str, optional) – overrides the instance-level cfgstr
- Returns
bool
- existing_versions()[source]¶
Returns data with different cfgstr values that were previously computed with this cacher.
- Yields
str – paths to cached files corresponding to this cacher
Example
>>> from ubelt.util_cache import Cacher >>> # Ensure that some data exists >>> known_fpaths = set() >>> import ubelt as ub >>> dpath = ub.ensure_app_cache_dir('ubelt', >>> 'test-existing-versions') >>> ub.delete(dpath) # start fresh >>> cacher = Cacher('versioned_data_v2', depends='1', dpath=dpath) >>> cacher.ensure(lambda: 'data1') >>> known_fpaths.add(cacher.get_fpath()) >>> cacher = Cacher('versioned_data_v2', depends='2', dpath=dpath) >>> cacher.ensure(lambda: 'data2') >>> known_fpaths.add(cacher.get_fpath()) >>> # List previously computed configs for this type >>> from os.path import basename >>> cacher = Cacher('versioned_data_v2', depends='2', dpath=dpath) >>> exist_fpaths = set(cacher.existing_versions()) >>> exist_fnames = list(map(basename, exist_fpaths)) >>> print('exist_fnames = {!r}'.format(exist_fnames)) >>> assert exist_fpaths.issubset(known_fpaths)
- clear(cfgstr=None)[source]¶
Removes the saved cache and metadata from disk
- Parameters
cfgstr (str, optional) – overrides the instance-level cfgstr
- tryload(cfgstr=None, on_error='raise')[source]¶
Like load, but returns None if the load fails due to a cache miss.
- Parameters
cfgstr (str, optional) – overrides the instance-level cfgstr
on_error (str, default=’raise’) – How to handle non-io errors errors. Either ‘raise’, which re-raises the exception, or ‘clear’ which deletes the cache and returns None.
- Returns
the cached data if it exists, otherwise returns None
- Return type
None | object
- load(cfgstr=None)[source]¶
Load the data cached and raise an error if something goes wrong.
- Parameters
cfgstr (str, optional) – overrides the instance-level cfgstr
- Returns
the cached data
- Return type
object
- Raises
IOError - if the data is unable to be loaded. This could be due to – a cache miss or because the cache is disabled.
Example
>>> from ubelt.util_cache import * # NOQA >>> # Setting the cacher as enabled=False turns it off >>> cacher = Cacher('test_disabled_load', '', enabled=True) >>> cacher.save('data') >>> assert cacher.load() == 'data' >>> cacher.enabled = False >>> assert cacher.tryload() is None
- save(data, cfgstr=None)[source]¶
Writes data to path specified by self.fpath(cfgstr).
Metadata containing information about the cache will also be appended to an adjacent file with the .meta suffix.
- Parameters
data (object) – arbitrary pickleable object to be cached
cfgstr (str, optional) – overrides the instance-level cfgstr
Example
>>> from ubelt.util_cache import * # NOQA >>> # Normal functioning >>> depends = 'long-cfg' * 32 >>> cacher = Cacher('test_enabled_save', depends=depends) >>> cacher.save('data') >>> assert exists(cacher.get_fpath()), 'should be enabeled' >>> assert exists(cacher.get_fpath() + '.meta'), 'missing metadata' >>> # Setting the cacher as enabled=False turns it off >>> cacher2 = Cacher('test_disabled_save', 'params', enabled=False) >>> cacher2.save('data') >>> assert not exists(cacher2.get_fpath()), 'should be disabled'
- ensure(func, *args, **kwargs)[source]¶
Wraps around a function. A cfgstr must be stored in the base cacher.
- Parameters
func (callable) – function that will compute data on cache miss
*args – passed to func
**kwargs – passed to func
Example
>>> from ubelt.util_cache import * # NOQA >>> def func(): >>> return 'expensive result' >>> fname = 'test_cacher_ensure' >>> depends = 'func params' >>> cacher = Cacher(fname, depends=depends) >>> cacher.clear() >>> data1 = cacher.ensure(func) >>> data2 = cacher.ensure(func) >>> assert data1 == 'expensive result' >>> assert data1 == data2 >>> cacher.clear()
- class ubelt.util_cache.CacheStamp(fname, dpath, cfgstr=None, product=None, hasher='sha1', verbose=None, enabled=True, depends=None, meta=None)[source]¶
Bases:
object
Quickly determine if a file-producing computation has been done.
Writes a file that marks that a procedure has been done by writing a “stamp” file to disk. Removing the stamp file will force recomputation. However, removing or changing the result of the computation may not trigger recomputation unless specific handling is done or the expected “product” of the computation is a file and registered with the stamper. If hasher is None, we only check if the product exists, and we ignore its hash, otherwise it checks that the hash of the product is the same.
- Parameters
fname (str) – Name of the stamp file
cfgstr (str) – Configuration associated with the stamped computation. A common pattern is to call
ubelt.hash_data()
on a dependency list.Deprecated in favor of depends. Indicates the state. Either this string or a hash of this string will be used to identify the cache. A cfgstr should always be reasonably readable, thus it is good practice to hash extremely detailed cfgstrs to a reasonable readable level. Use meta to store make original details persist.
dpath (PathLike) – Where to store the cached stamp file
product (PathLike or Sequence[PathLike], optional) – Path or paths that we expect the computation to produce. If specified the hash of the paths are stored.
hasher (str, default=’sha1’) – The type of hasher used to compute the file hash of product. If None, then we assume the file has not been corrupted or changed. Defaults to sha1.
verbose (bool, default=None) – Passed to internal ub.Cacher object
enabled (bool, default=True) – if False, expired always returns True
depends (str | List[str]) – Indicate dependencies of this cache. If the dependencies change, then the cache is recomputed. New to CacheStamp in version 0.9.2, replaces cfgstr.
meta (object) – Metadata that is also saved with the
cfgstr
. This can be useful to indicate how thecfgstr
was constructed. New to CacheStamp in version 0.9.2.
Todo
[ ] expiration time delta or date time (also remember when renewed)
Example
>>> import ubelt as ub >>> from os.path import join >>> # Stamp the computation of expensive-to-compute.txt >>> dpath = ub.ensure_app_cache_dir('ubelt', 'test-cache-stamp') >>> ub.delete(dpath) >>> ub.ensuredir(dpath) >>> product = join(dpath, 'expensive-to-compute.txt') >>> self = CacheStamp('somedata', depends='someconfig', dpath=dpath, >>> product=product, hasher=None) >>> self.hasher = None >>> if self.expired(): >>> ub.writeto(product, 'very expensive') >>> self.renew() >>> assert not self.expired() >>> # corrupting the output will not expire in non-robust mode >>> ub.writeto(product, 'corrupted') >>> assert not self.expired() >>> self.hasher = 'sha1' >>> # but it will expire if we are in robust mode >>> assert self.expired() >>> # deleting the product will cause expiration in any mode >>> self.hasher = None >>> ub.delete(product) >>> assert self.expired()
- expired(cfgstr=None, product=None)[source]¶
Check to see if a previously existing stamp is still valid and if the expected result of that computation still exists.
- Parameters
cfgstr (str, optional) – overrides the instance-level cfgstr
product (PathLike or Sequence[PathLike], optional) – override the default product if specified
- Returns
True if the stamp is invalid or does not exist.
- Return type
bool