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    <p>I don't actually think that DI/IoC are <em>that</em> uncommon in Python. What <em>is</em> uncommon, however, are DI/IoC <em>frameworks/containers</em>.</p> <p>Think about it: what does a DI container do? It allows you to </p> <ol> <li>wire together independent components into a complete application ...</li> <li>... at runtime.</li> </ol> <p>We have names for "wiring together" and "at runtime":</p> <ol> <li>scripting</li> <li>dynamic</li> </ol> <p>So, a DI container is nothing but an interpreter for a dynamic scripting language. Actually, let me rephrase that: a typical Java/.NET DI container is nothing but a crappy interpreter for a really bad dynamic scripting language with butt-ugly, sometimes XML-based, syntax.</p> <p>When you program in Python, why would you want to use an ugly, bad scripting language when you have a beautiful, brilliant scripting language at your disposal? Actually, that's a more general question: when you program in pretty much any language, why would you want to use an ugly, bad scripting language when you have Jython and IronPython at your disposal?</p> <p>So, to recap: the <em>practice</em> of DI/IoC is just as important in Python as it is in Java, for exactly the same reasons. The <em>implementation</em> of DI/IoC however, is built into the language and often so lightweight that it completely vanishes. </p> <p>(Here's a brief aside for an analogy: in assembly, a subroutine call is a pretty major deal - you have to save your local variables and registers to memory, save your return address somewhere, change the instruction pointer to the subroutine you are calling, arrange for it to somehow jump back into your subroutine when it is finished, put the arguments somewhere where the callee can find them, and so on. IOW: in assembly, "subroutine call" is a Design Pattern, and before there were languages like Fortran which had subroutine calls built in, people were building their own "subroutine frameworks". Would you say that subroutine calls are "uncommon" in Python, just because you don't use subroutine frameworks?)</p> <p>BTW: for an example of what it looks like to take DI to its logical conclusion, take a look at <a href="http://GBracha.BlogSpot.Com/" rel="noreferrer">Gilad Bracha</a>'s <a href="http://NewspeakLanguage.Org/" rel="noreferrer">Newspeak Programming Language</a> and his writings on the subject:</p> <ul> <li><a href="http://GBracha.BlogSpot.Com/2007/06/constructors-considered-harmful.html" rel="noreferrer">Constructors Considered Harmful</a></li> <li><a href="http://GBracha.BlogSpot.Com/2007/12/some-months-ago-i-wrote-couple-of-posts.html" rel="noreferrer">Lethal Injection</a></li> <li><a href="http://GBracha.BlogSpot.Com/2009/06/ban-on-imports.html" rel="noreferrer">A Ban on Imports</a> (<a href="http://GBracha.BlogSpot.Com/2009/07/ban-on-imports-continued.html" rel="noreferrer">continued</a>)</li> </ul>
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    1. POWhy is IoC / DI not common in Python?
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    1. COWhile I agree. The XML comment is wrong. Many (at least the modern) IOC containers use convention (code) over configuration (XML).
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    2. COThere's nothing preventing you from writing the wiring explicitly in Java, but as you have more and more services, dependencies get more complex. A DI container is like Make: you declare the dependencies and the container initializes them in the right order. Guice is a Java DI framework where everything is written in Java code. By writing declaratively a DI container also adds support for post processing the declerations before initialization (e.g., replace property placeholders with actual values)
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    3. CO"The implementation of DI/IoC however, is built into the language and often so lightweight that it completely vanishes." Down vote because this is categorically untrue. DI is a pattern where an interface is passed in to the constructor. It is not built-in in python.
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