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Diffstat (limited to 'Doc/whatsnew/3.2.rst')
| -rw-r--r-- | Doc/whatsnew/3.2.rst | 37 |
1 files changed, 24 insertions, 13 deletions
diff --git a/Doc/whatsnew/3.2.rst b/Doc/whatsnew/3.2.rst index 62fb18f..12d3527 100644 --- a/Doc/whatsnew/3.2.rst +++ b/Doc/whatsnew/3.2.rst @@ -71,8 +71,8 @@ New, Improved, and Deprecated Modules save repeated queries to an external resource whenever the results are expected to be the same. - For example, adding an LFU decorator to a database query function can save - database accesses for the most popular searches:: + For example, adding a caching decorator to a database query function can save + database accesses for popular searches:: @functools.lfu_cache(maxsize=50) def get_phone_number(name): @@ -80,21 +80,32 @@ New, Improved, and Deprecated Modules c.execute('SELECT phonenumber FROM phonelist WHERE name=?', (name,)) return c.fetchone()[0] - The LFU (least-frequently-used) cache gives best results when the distribution - of popular queries tends to remain the same over time. In contrast, the LRU - (least-recently-used) cache gives best results when the distribution changes - over time (for example, the most popular news articles change each day as - newer articles are added). + The caches support two strategies for limiting their size to *maxsize*. The + LFU (least-frequently-used) cache works bests when popular queries remain the + same over time. In contrast, the LRU (least-recently-used) cache works best + query popularity changes over time (for example, the most popular news + articles change each day as newer articles are added). - The two caching decorators can be composed (nested) to handle hybrid cases - that have both long-term access patterns and some short-term access trends. + The two caching decorators can be composed (nested) to handle hybrid cases. For example, music searches can reflect both long-term patterns (popular classics) and short-term trends (new releases):: - @functools.lfu_cache(maxsize=500) - @functools.lru_cache(maxsize=100) - def find_music(song): - ... + @functools.lfu_cache(maxsize=500) + @functools.lru_cache(maxsize=100) + def find_lyrics(song): + query = 'http://www.example.com/songlist/%s' % urllib.quote(song) + page = urllib.urlopen(query).read() + return parse_lyrics(page) + + To help with choosing an effective cache size, the wrapped function + is instrumented with two attributes 'hits' and 'misses':: + + >>> for song in user_requests: + ... find_lyrics(song) + >>> print find_lyrics.hits + 4805 + >>> print find_lyrics.misses + 980 (Contributed by Raymond Hettinger) |