A possible bug related to parsing

[RCU]

Hello,
I would like to report a bug I got while running ShedSkin.
I am not sure it's really Shedskin - it looks to me actually the problem comes from
the compiler module.
You can reproduce the error by running the attached Python script.

The problem is the following: although ShedSkin treats well global vars declared and
used inside functions, if a global var is used as iterator in a for statement, then
ShedSkin is considering that variable to be local to the function. Therefore, the
local-considered variable will obstruct the global, which will lead to different behavior
in the function with the for statement in C++ as oposed to Python.
You can see that by running:
- the Python script directly
- the resulting C++ code from ShedSkin for the Python script.
Note that the boing() Python function has:
global day
while the C++ translation of boing is:
__ss_int boing(__ss_int c, double d) {
__ss_int __0, __1, day, sum;

The reason this happens is that day is reported as a (local) variable of function
boing() by func.vars.items() in module cpp.py, method local_defs(self, func) .
I looked a bit in Python/Lib/compiler (module ast.py), but I couldn't figure out
where the result of func.vars.items() is really created.

Could you please take a look and see if I am missing something?

Note that I run ShedSkin on Python 2.7.2, which comes with Ubuntu 11.10. I've tested
also a bit on Python 2.5.4 and 2.6.6.

Best regards,
Alex

[Mark Dufour]

hi alex,

good catch! :D it's a shedskin bug, and just in time for 0.9.4. I will see if I can fix the problem tomorrow. or if you like, I could try to give you some pointers so you might be able to fix the problem yourself..?

thanks again!

mark.

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[srepmub]

hi alex,

sorry I'm always a bit impatient :P the problem is now fixed in git!

thanks again for reporting!
mark.

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[RCU]

Hi.
Sorry for the late reply.

Glad to know you solved it.
I looked in git for the latest code - is the changed you performed to fix this bug
found in cpp.py, def local_defs(self, func) ?

Best regards,
Alex

On 6/4/2013 12:36 PM, Mark Dufour wrote:
> hi alex,
>
> good catch! :D it's a shedskin bug, and just in time for 0.9.4. I will see if I can fix

Interesting. It looked to me that ShedSkin is not really the culprit.

> the problem tomorrow. or if you like, I could try to give you some pointers so you might
> be able to fix the problem yourself..?
>
> thanks again!
> mark.

> http://www.youtube.com/watch?v=E6LsfnBmdnk <http://www.youtube.com/watch?v=E6LsfnBmdnk>

>
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[Mark Dufour]

hi alex,

git show a9fa2ac

[..]

+    def default_var(self, name, func):
+        if isinstance(func, Function) and name in func.globals:
+            return default_var(self.gx, name, None, mv=getmv())
+        else:
+            return default_var(self.gx, name, func, mv=getmv())
+

this check was not done consistently before. so it missed in some cases that a variable was declared global.

thanks!

mark.

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