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Diffstat (limited to 'Doc/whatsnew/3.2.rst')
| -rw-r--r-- | Doc/whatsnew/3.2.rst | 43 |
1 files changed, 15 insertions, 28 deletions
diff --git a/Doc/whatsnew/3.2.rst b/Doc/whatsnew/3.2.rst index bc31764..2c625a8 100644 --- a/Doc/whatsnew/3.2.rst +++ b/Doc/whatsnew/3.2.rst @@ -66,45 +66,32 @@ Some smaller changes made to the core Python language are: New, Improved, and Deprecated Modules ===================================== -* The functools module now includes two new decorators for caching function - calls, :func:`functools.lru_cache` and :func:`functools.lfu_cache`. These can - save repeated queries to an external resource whenever the results are - expected to be the same. +* The functools module now includes a new decorator for caching function calls. + :func:`functools.lru_cache` can save repeated queries to an external resource + whenever the results are expected to be the same. For example, adding a caching decorator to a database query function can save database accesses for popular searches:: - @functools.lfu_cache(maxsize=50) + @functools.lru_cache(maxsize=300) def get_phone_number(name): c = conn.cursor() c.execute('SELECT phonenumber FROM phonelist WHERE name=?', (name,)) return c.fetchone()[0] - 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. - 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_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, find_lyrics.misses) + To help with choosing an effective cache size, the wrapped function is + instrumented with two attributes *hits* and *misses*:: + + >>> for name in user_requests: + ... get_phone_number(name) + >>> print(get_phone_number.hits, get_phone_number.misses) 4805 980 + If the phonelist table gets updated, the outdated contents of the cache can be + cleared with:: + + >>> get_phone_number.clear() + (Contributed by Raymond Hettinger) * The previously deprecated :func:`contextlib.nested` function has been |