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Date: Wed, 29 May 2013 09:30:58 -0300
Subject: Re: Fatal Python error
From: Marcel Rodrigues <marcelgmr@gmail.com>
To: Joshua Landau <joshua.landau.ws@gmail.com>
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I just tried your code with similar results: it does nothing on PyPy
2.0.0-beta2 and Python 2.7.4. But on Python 3.3.1 it caused core dump.
It's a little weird but so is the code. You have defined a function that
calls itself unconditionally. This will cause a stack overflow, which is a
RuntimeError.
 Since you are handling this very exception with a pass statement, we would
expect that no error occurs. But the fatal error message seems pretty
informative at this point: "Cannot recover from stack overflow.".

One thing to note is that while it's reasonable to handle exceptions that
happens at the level of your Python code, like a ValueError, it's not so
reasonable to try to handle something that may disturb the interpreter
itself in a lower level, like a stack overflow (I think that the stack used
by your code is the same stack used by the interpreter code, but I'm not
sure).


2013/5/29 Joshua Landau <joshua.landau.ws@gmail.com>

> Hello all, again. Instead of revising like I'm meant to be, I've been
> delving into a bit of Python and I've come up with this code:
>
> class ClassWithProperty:
>  @property
> def property(self):
> pass
>
> thingwithproperty = ClassWithProperty()
>
> def loop():
> try:
> thingwithproperty.property
>  except:
> pass
>
> loop()
>
> try:
> loop()
> except RuntimeError:
> pass
>
> As you will expect, this does nothing... on Python2.7 and PyPy. Python3.3
> prefers to spit out a "Fatal Python error: Cannot recover from stack
> overflow.", which seems a bit unexpected.
>
> Wuzzup with that?
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
>

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<div dir=3D"ltr"><div><div>I just tried your code with similar results: it =
does nothing on PyPy 2.0.0-beta2 and Python 2.7.4. But on Python 3.3.1 it c=
aused core dump.<br></div>It&#39;s a little weird but so is the code. You h=
ave defined a function that calls itself unconditionally. This will cause a=
 stack overflow, which is a RuntimeError.<br>
</div><div>=C2=A0Since you are handling this very exception with a pass sta=
tement, we would expect that no error occurs. But the fatal error message s=
eems pretty informative at this point: &quot;Cannot recover from stack over=
flow.&quot;.<br>
<br>One thing to note is that while it&#39;s reasonable to handle exception=
s that happens at the level of your Python code, like a ValueError, it&#39;=
s not so reasonable to try to handle something that may disturb the interpr=
eter itself in a lower level, like a stack overflow (I think that the stack=
 used by your code is the same stack used by the interpreter code, but I=
9;m not sure).<br>
</div></div><div class=3D"gmail_extra"><br><br><div class=3D"gmail_quote">2=
013/5/29 Joshua Landau <span dir=3D"ltr">&lt;<a href=3D"mailto:joshua.landa=
u.ws@gmail.com" target=3D"_blank">joshua.landau.ws@gmail.com</a>&gt;</span>=
<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-lef=
t:1px #ccc solid;padding-left:1ex">
<div dir=3D"ltr">Hello all, again. Instead of revising like I&#39;m meant t=
o be, I&#39;ve been delving into a bit of Python and I&#39;ve come up with =
this code:<div><br></div><div><div><div>class ClassWithProperty:</div><div>


<span style=3D"white-space:pre-wrap">	</span>@property</div><div><span styl=
e=3D"white-space:pre-wrap">	</span>def property(self):</div><div><span styl=
e=3D"white-space:pre-wrap">		</span>pass</div><div><br></div><div>

thingwithproperty =3D ClassWithProperty()</div><div><br></div><div>def loop=
():</div><div><span style=3D"white-space:pre-wrap">	</span>try:</div><div><=
span style=3D"white-space:pre-wrap">		</span>thingwithproperty.property</di=
v>


<div><span style=3D"white-space:pre-wrap">	</span>except:</div><div><span s=
tyle=3D"white-space:pre-wrap">		</span>pass</div><div><br></div><div><span =
style=3D"white-space:pre-wrap">	</span>loop()</div><div><br></div>

<div>try:</div><div><span style=3D"white-space:pre-wrap">	</span>loop()</di=
v><div>except RuntimeError:</div><div><span style=3D"white-space:pre-wrap">=
	</span>pass</div></div></div><div><br></div><div>As you will expect, this =
does nothing... on Python2.7 and PyPy. Python3.3 prefers to spit out a &quo=
t;Fatal Python error: Cannot recover from stack overflow.&quot;, which seem=
s a bit unexpected.</div>


<div><br></div><div>Wuzzup with that?</div></div>
<br>--<br>
<a href=3D"http://mail.python.org/mailman/listinfo/python-list" target=3D"_=
blank">http://mail.python.org/mailman/listinfo/python-list</a><br>
<br></blockquote></div><br></div>

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