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2013-12-27T08:00:48.307
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2013-12-27T09:31:24.713
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<code>isinstance(obj, some_class)</code> just iterates up obj's inheritance chain, looking for <code>some_class</code>. Thus <code>isinstance(file_like, io.IOBase)</code>, will be false, as your <code>file_like</code> class doesn't have <code>io.IOBase</code> in its ancestry. <code>file_like</code> doesn't designate an explicit parent, hence it implicitly inherits only from <code>object</code>. That's the only class - besides <code>file_like</code> itself - that will test positive for a <code>file_like</code> instance with <code>isinstance()</code>. What you are doing in <code>file_like</code> is defining the methods expected on a file-like object while not inheriting from any particular "file-like" class. This approach is called <a href="http://en.wikipedia.org/wiki/Duck_typing" rel="nofollow">duck-typing</a>, and it has many merits in dynamic languages, although it's more popular in others (e.g. Ruby) than Python. Still, if whatever you're providing your <code>file_like</code> instance to follows duck-typing, it should work, provided your <code>file_like</code> does in fact "quack like a file", i.e. behaves sufficiently like a file to not cause errors upon usage at the receiving end. Of course, if the receiving end is not following duck-typing, for example tries to check types by <code>isinstance()</code> as you do here, this approach will fail. Finally, a small stylistic nit: don't put empty parens on a class if it doesn't inherit anything explicitly. They are redundant.
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1. POHow to make a file-like class work with "isinstance(cls, io.IOBase)"?
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1. USDun Peal
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1. USDun Peal
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1. COThanks for your answer. It cleared up many of my questions. Thanks also for the style note, I believe it's a carryover from functions which requires parens. I'll take note of it
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