Add example, tighten text, and minor clean-ups.
diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst
index 5b65874..7c9b9ca 100644
--- a/Doc/library/functools.rst
+++ b/Doc/library/functools.rst
@@ -42,40 +42,52 @@
.. versionadded:: 3.2
-.. decorator:: lru_cache(maxsize)
+.. decorator:: lru_cache(maxsize=100)
Decorator to wrap a function with a memoizing callable that saves up to the
*maxsize* most recent calls. It can save time when an expensive or I/O bound
function is periodically called with the same arguments.
- The *maxsize* parameter defaults to 100. Since a dictionary is used to cache
- results, the positional and keyword arguments to the function must be
- hashable.
+ Since a dictionary is used to cache results, the positional and keyword
+ arguments to the function must be hashable.
- The wrapped function is instrumented with a :attr:`cache_info` attribute that
- can be called to retrieve a named tuple with the following fields:
+ To help measure the effectiveness of the cache and tune the *maxsize*
+ parameter, the wrapped function is instrumented with a :func:`cache_info`
+ function that returns a :term:`named tuple` showing *hits*, *misses*,
+ *maxsize* and *currsize*.
- - :attr:`maxsize`: maximum cache size (as set by the *maxsize* parameter)
- - :attr:`size`: current number of entries in the cache
- - :attr:`hits`: number of successful cache lookups
- - :attr:`misses`: number of unsuccessful cache lookups.
-
- These statistics are helpful for tuning the *maxsize* parameter and for measuring
- the effectiveness of the cache.
-
- The wrapped function also has a :attr:`cache_clear` attribute which can be
- called (with no arguments) to clear the cache.
+ The decorator also provides a :func:`cache_clear` function for clearing or
+ invalidating the cache.
The original underlying function is accessible through the
- :attr:`__wrapped__` attribute. This allows introspection, bypassing
- the cache, or rewrapping the function with a different caching tool.
+ :attr:`__wrapped__` attribute. This is useful for introspection, for
+ bypassing the cache, or for rewrapping the function with a different cache.
A `LRU (least recently used) cache
- <http://en.wikipedia.org/wiki/Cache_algorithms#Least_Recently_Used>`_
- works best when more recent calls are the best predictors of upcoming calls
- (for example, the most popular articles on a news server tend to
- change each day). The cache's size limit assurs that caching does not
- grow without bound on long-running processes such as web servers.
+ <http://en.wikipedia.org/wiki/Cache_algorithms#Least_Recently_Used>`_ works
+ best when more recent calls are the best predictors of upcoming calls (for
+ example, the most popular articles on a news server tend to change daily).
+ The cache's size limit assures that the cache does not grow without bound on
+ long-running processes such as web servers.
+
+ Example -- Caching static web content::
+
+ @functools.lru_cache(maxsize=20)
+ def get_pep(num):
+ 'Retrieve text of a Python Enhancement Proposal'
+ resource = 'http://www.python.org/dev/peps/pep-%04d/' % num
+ try:
+ with urllib.request.urlopen(resource) as s:
+ return s.read()
+ except urllib.error.HTTPError:
+ return 'Not Found'
+
+ >>> for n in 8, 290, 308, 320, 8, 218, 320, 279, 289, 320, 9991:
+ ... pep = get_pep(n)
+ ... print(n, len(pep))
+
+ >>> print(get_pep.cache_info())
+ CacheInfo(hits=3, misses=8, maxsize=20, currsize=8)
.. versionadded:: 3.2