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POPython decorators
 

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    <p>I have a question about decorators. I understand what are decorators and I know how to use it, I have read all this tutorial <a href="https://stackoverflow.com/questions/739654/how-can-i-make-a-chain-of-function-decorators-in-python?lq=1">How to make a chain of function decorators?</a></p> <p>I understand that :</p> <pre><code>&gt;&gt;&gt; def my_decorator(fn): &gt;&gt;&gt; print 'Do something before' &gt;&gt;&gt; print fn() &gt;&gt;&gt; def foo(): &gt;&gt;&gt; return 'Hello World!' &gt;&gt;&gt; foo = my_decorator(foo) </code></pre> <p>Is the same at that :</p> <pre><code>&gt;&gt;&gt; def my_decorator(fn): &gt;&gt;&gt; print 'Do something before' &gt;&gt;&gt; print fn() &gt;&gt;&gt; @my_decorator &gt;&gt;&gt; def foo(): &gt;&gt;&gt; return 'Hello World!' </code></pre> <p>I know what are closures and why we use closure in a decorator with parameters (to get the decorator parameters in nested function) but that I don't understand is why we use closure and nested functions to get arguments and the function.</p> <p>How the closure (or something else) can access parameters and the function outside. I am unable to do the same without the @decorator.</p> <p>Here for example I can access my foo() and the parameters of the function without passing this function in parameter :</p> <pre><code>def my_decorator(str): def wrapper(fn): def inner_function(*args): print 'Do something before' return fn(*args) return inner_function return wrapper @my_decorator('test') def foo(a, b): return a + b print foo(1, 1) </code></pre> <p>How this is possible ?</p>
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    1. COBecause that's what a decorator does. It's not a simple function call, it's a decorator, and it gets passed the function below it as the first argument (and the returned function replaces it).
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    2. COand it's magic ?
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    3. COIt's not magic exactly - it's like asking why the brackets after a function call it - it's a documented part of the language.
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