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PO"MetaClass", "__new__", "cls" and "super" - what is the mechanism exactly?
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copied!<p>I have read posts like these:</p> <ol> <li><a href="https://stackoverflow.com/questions/100003/what-is-a-metaclass-in-python">What is a metaclass in Python?</a> </li> <li><a href="https://stackoverflow.com/questions/392160/what-are-your-concrete-use-cases-for-metaclasses-in-python">What are your (concrete) use-cases for metaclasses in Python?</a></li> <li><a href="http://fuhm.net/super-harmful/" rel="nofollow noreferrer">Python's Super is nifty, but you can't use it</a></li> </ol> <p>But somehow I got confused. Many confusions like:</p> <p>When and why would I have to do something like the following?</p> <pre><code># Refer link1 return super(MyType, cls).__new__(cls, name, bases, newattrs) </code></pre> <p>or</p> <pre><code># Refer link2 return super(MetaSingleton, cls).__call__(*args, **kw) </code></pre> <p>or</p> <pre><code># Refer link2 return type(self.__name__ + other.__name__, (self, other), {}) </code></pre> <p>How does super work exactly?</p> <p>What is class registry and unregistry in link1 and how exactly does it work? (I thought it has something to do with <a href="http://en.wikipedia.org/wiki/Singleton_pattern" rel="nofollow noreferrer">singleton</a>. I may be wrong, being from C background. My coding style is still a mix of functional and OO).</p> <p>What is the flow of class instantiation (subclass, metaclass, super, type) and method invocation (</p> <pre><code>metaclass->__new__, metaclass->__init__, super->__new__, subclass->__init__ inherited from metaclass </code></pre> <p>) with well-commented working code (though the first link is quite close, but it does not talk about cls keyword and super(..) and registry). Preferably an example with multiple inheritance.</p> <p>P.S.: I made the last part as code because Stack Overflow formatting was converting the text <code>metaclass->__new__</code> to metaclass-><strong>new</strong></p>

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