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    <p>from the <a href="http://docs.python.org/2/reference/datamodel.html#object.__exit__">Data model entry for <code>object.__exit__</code></a></p> <blockquote> <p>If an exception is supplied, and the method wishes to suppress the exception (i.e., prevent it from being propagated), it should return a true value. Otherwise, the exception will be processed normally upon exit from this method.</p> </blockquote> <p>In your <code>__exit__</code> function, you're returning <code>True</code> which will suppress <em>all</em> exceptions. If you change it to return <code>False</code>, the exceptions will continue to be raised as normal (with the only difference being that you guarantee that your <code>__exit__</code> function gets called and you can make sure to clean up after yourself)</p> <p>For example, changing the code to:</p> <pre><code>def __exit__(self, exctype, value, tb): print " __exit__; excptype: '%s'; value: '%s'" % (exctype, value) if exctype is GeneratorExit: return False return True </code></pre> <p>allows you to do the right thing and not suppress the <code>GeneratorExit</code>. Now you <em>only</em> see the attribute error. Maybe the rule of thumb should be the same as with any Exception handling -- <strong>only intercept Exceptions if you know how to handle them</strong>. Having an <code>__exit__</code> return <code>True</code> is on par (maybe slightly worse!) than having a bare except:</p> <pre><code>try: something() except: #Uh-Oh pass </code></pre> <hr> <p>Note that when the <code>AttributeError</code> is raised (and not caught), I believe that causes the reference count on your generator object to drop to 0 which then triggers a <code>GeneratorExit</code> exception within the generator so that it can clean itself up. Using my <code>__exit__</code>, play around with the following two cases and hopefully you'll see what I mean:</p> <pre><code>try: for item in foo(10): print 'Fail - val: %d' % item.val item.not_an_attribute except AttributeError: pass print "Here" #No reference to the generator left. #Should see __exit__ before "Here" </code></pre> <p>and</p> <pre><code>g = foo(10) try: for item in g: print 'Fail - val: %d' % item.val item.not_an_attribute except AttributeError: pass print "Here" b = g #keep a reference to prevent the reference counter from cleaning this up. #Now we see __exit__ *after* "Here" </code></pre>
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    1. POHow to use a python context manager inside a generator
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    1. CO@mgilson Thanks for your great answer. It seems that the generator function is not what catches the attribute error. That is the behavior that I wanted, but it seems it is not possible. I want to use one with-statement to centralize the exception handling in a sequence of generators.
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    2. CO@David -- context managers are something that I've been working with a decent amount as of late, so they're fresh on my mind :). It was a good question. I wish all new users asked such nice first questions :).
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    3. CO@lukecampbell -- I'm glad you liked it :). It was an interesting question for sure.
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