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POWhy do Python doctests require isinstance to use matching qualified/unqualified naming?
 

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  1. POWhy do Python doctests require isinstance to use matching qualified/unqualified naming?
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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/13181559/importing-modules-main-vs-import-as-module">Importing modules: __main__ vs import as module</a> </p> </blockquote> <p>I am aware that in most cases <code>isinstance</code> is not needed or should be avoided (e.g., <a href="https://stackoverflow.com/questions/3111611/is-this-use-of-isinstance-pythonic-good">Is this use of isinstance pythonic/&quot;good&quot;?</a>). However, sometimes it is what I need. </p> <p>In both Python 2.6, 2.7, and 3.2, however, I have noticed the following irregularity in how <code>isinstance</code> works between execution in doctests and normal execution. </p> <p>For example, I expect the following behavior, where <code>isinstance</code> is ambivalent to whether I am using qualified or unqualified names:</p> <pre><code>import collections from collections import OrderedDict assert isinstance(collections.OrderedDict(), collections.OrderedDict) == True assert isinstance(collections.OrderedDict(), OrderedDict) == True </code></pre> <p>The same code, executed within a Doctest, works just the same.</p> <p>However, if I define a class within a module named "isinstanceTest.py" and define a function within the same module that uses <code>isinstance</code> to match that class, things get more interesting. The following doctest is written to pass. I am using the <code>unittest.TextTestRunner</code> as I routinely gather and run my doctests and unittests across many modules together in one suite.</p> <pre><code>import unittest, doctest import collections class A: pass def isinstance_A(arg): ''' &gt;&gt;&gt; import isinstanceTest &gt;&gt;&gt; isinstanceTest.isinstance_A(isinstanceTest.A()) True &gt;&gt;&gt; isinstance_A(A()) True &gt;&gt;&gt; isinstanceTest.isinstance_A(A()) False &gt;&gt;&gt; isinstance_A(isinstanceTest.A()) False ''' return isinstance(arg, A) if __name__ == '__main__': l = doctest.DocTestSuite(__name__) runner = unittest.TextTestRunner() runner.run(l) </code></pre> <p>Notice that the last two doctest statements, where both qualified and unqualified names are used, produce unexpected results. </p> <p>If, while in the directory where "isinstanceTest.py" lives, I open an interpreter and execute equivalent commands, results are as expected:</p> <pre><code>Python 3.2.3 (default, May 3 2012, 15:51:42) [GCC 4.6.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. &gt;&gt;&gt; import isinstanceTest &gt;&gt;&gt; from isinstanceTest import * &gt;&gt;&gt; isinstanceTest.isinstance_A(isinstanceTest.A()) True &gt;&gt;&gt; isinstance_A(A()) True &gt;&gt;&gt; isinstanceTest.isinstance_A(A()) True &gt;&gt;&gt; isinstance_A(isinstanceTest.A()) True </code></pre> <p>So while this behavior is consistent and localized to running doctests in test suites (and I have coded around it as necessary, and generally only use qualified names in doctests anyways), the larger question is: is this a documented limitation of doctests (I have not yet found any docs that mention this), or is this a bug? </p>
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    1. CONote that adding `>>> from isinstanceTest import *` to the doctest permits correct results to be returned; yet, this import is not needed to use the unqualfied names `A` and `isinstance_A`.
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    2. CO`__main__.A` is not the same class as `isinstanceTest.A`; do not mix importing from the local script with accessing the same names via globals.
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      1. USMartijn Pieters
 

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