[pypy-dev] [sympy] Re: sympy tests: pypy vs cpython incompatibilities

[Ondrej Certik]

On Sat, Oct 11, 2008 at 8:13 PM, didier deshommes <dfdeshom at gmail.com> wrote:
>
> On Sat, Oct 11, 2008 at 1:50 PM, Ondrej Certik <ondrej at certik.cz> wrote:
>>> as soon as someone realizes that in CPython it is possible to speed up
>>> iteration over strings by creating a stringiterator type, then CPython
>>> will grow a 'str.__iter__' as well, and the same infinite recursion will
>>> occur in sympy...
>>>
>>> A cleaner way to say "is x iterable?" would be to try to call iter(x)
>>> and see if it raises TypeError or not.
>>
>> Indeed, thanks very much for the tip. We'll fix that, that's
>> definitely something that should be fixed in sympy, I created a new
>> issue for that:
>
> Hi,
> I've faced the same problem and checking if x has the __getitem__
> attribute has worked for me. The rationale being that any iterable has
> a way to access its individual items.

Thanks Didier for the tip. Both iter("p") and "p".__getitem__ behaves
the same in both python and pypy. But "p".__iter__ behaves differently
and our code assumed that "p" is not iterable, so I just implemented a
function:

http://code.google.com/p/sympy/issues/detail?id=1153#c1

+def is_iterable(x):
+    try:
+        iter(x)
+        if isinstance(x, str) and len(x) == 1:
+            return False
+        return True
+    except TypeError:
+        return False


Which fixes the problem above. Unfortunately, then there are other
unrelated problems.

Armin, is there some way to tell pypy-c to stop on ctrl-C? I am
getting hangups and the only way out is to kill the pypy-c program.
It'd be much more convenient if I could just do ctrl-C and it would
print the stacktrace.

I'll be continuing porting sympy to pypy some other time, so anyone
feel free to take over it. You just need to apply the patch in the
issue 1153 and then try to make all tests to pass.

Thanks,
Ondrej