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<h1 id="python设计模式之单例模式"><a href="http://dongweiming.github.io/python-singleton.html"Permalink to python设计模式之单例模式"" target="_blank">python设计模式之单例模式</a></h1><h2 id="单例模式">单例模式</h2><p>通过Singleton模式，全局保证只有一个实例，在python中怎么用呢？</p><h2 id="python的例子">python的例子</h2><p>我这里实现了一个pymongo连接的‘缓存’,为了保证在一个进程里面调用只产生一个连接数</p><pre><code>class ConnectionSingleton(object):
'''通过重载实例化函数__new__缓存mongodb连接'''
conn=None
def __new__(cls,*args,**kwds):
if cls.conn is None:
cls.conn=pymongo.MongoClient()
return cls.conn</code></pre>
<p>调用的时候可以</p><pre><code>db = ConnectionSingleton()</code></pre>
<h2 id="和pymongo相关的温馨提示">和pymongo相关的温馨提示</h2><ol><li>请不要使用pymongo.Connection，官网不推荐，并且有个问题，当你close它的实例，连接数并没有立刻减少
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<li>做好数据库操作的类变量的封装，调用完毕要显式close/disconnect
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