[flask] 在blueprint中 使用 Flask-Cache 快取

Flask Cache

在開發flask 應用程式時，若是會往backend要很多次重複的資料，或是當service負載變重時，可以使用 flask cache 的方式，方便直接加上decorator 來採用 cache。

install Flask-Cache

pip install Flask-Cache

flask-cache for blueprint

cache.py

先準備一個 cache file

#coding=utf-8
from flask.ext.cache import Cache

cache = Cache(config={'CACHE_TYPE':'simple'})

• 可選的 CACHE_TYPE 可以參考 docs

Built-in cache types:

null: NullCache (default)
simple: SimpleCache
memcached: MemcachedCache (pylibmc or memcache required)
gaememcached: GAEMemcachedCache
redis: RedisCache (Werkzeug 0.7 required)
filesystem: FileSystemCache
saslmemcached: SASLMemcachedCache (pylibmc required)

views.py

在view 中使用 flask-cache

from cache import cache
#cache 的時間
CACHE_G_TIME=500

一個使用範例

class ListView(MethodView):
    @cache.cached(CACHE_G_TIME,key_prefix=make_cache_key)
    def get(self,page=1,board='',author='',long_mode=0):
        #posts=Post.objects.all()
        page=request.args.get('page', 1)
        per_page=request.args.get('per_page', 10)

def make_cache_key(*args, **kwargs):
    #print 'request url : %s ' % request.url
    return request.url

這邊可以特別注意的是，除了 timeout的設定以外，還有是用一個key_prefix func。 預設在Flask-Cache 內的 cache key 是 request path ,要是你的url 有帶其他的 parameter 會被是成同一個key，所以加上了key_prefix的func來處理帶有parameter 的 url。

cached(timeout=None, key_prefix='view/%s', unless=None)

Decorator. Use this to cache a function. By default the cache key is view/request.path. You are able to use this decorator with any function by changing the key_prefix. If the token %s is located within the key_prefix then it will replace that with request.path

使用了cache 以後在單位時間的同樣request都被cache起來，backend service著實減少不少負擔。

Ref:

• thadeusb/flask-cache https://github.com/thadeusb/flask-cache/
• Flask-Cache — Flask-Cache 0.13 documentation https://pythonhosted.org/Flask-Cache/
• Using Flask Cache | python | flask | BrunoRocha.org | Python web development http://brunorocha.org/python/flask/using-flask-cache.html
• python - Using flask extensions in flask blueprints - Stack Overflow http://stackoverflow.com/questions/11020170/using-flask-extensions-in-flask-blueprints
• python - What does key_prefix do for flask-cache? - Stack Overflow http://stackoverflow.com/questions/14228985/what-does-key-prefix-do-for-flask-cache

[python] " //= assignment operator"

What does the //= assignment operator do in Python - Stack Overflow
http://stackoverflow.com/questions/9493647/what-does-the-assignment-operator-do-in-python


9.9. operator — Standard operators as functions — Python 2.7.10rc0 documentation
https://docs.python.org/2/library/operator.html

For the code

x = 16
x //= 2

The value of x is 8. Basically, x = x // 2, integer division