Issue with list comprehension

[oroppas]

Hi,

The simple list comprehension does not seem to work.

libs = 'mkl , , openblas, blis, '
print(libs)
print([b for b in [a.strip() for a in libs.split(',')] if b])

CPython

mkl , , openblas, blis, 
['mkl', 'openblas', 'blis']

Graal Python

Traceback (most recent call last):
  File "/home/ryutas/graalpython/list_comprehension/test.py", line 3, in <module 'test.py'>
    print([b for b in [a.strip() for a in libs.split(',')] if b])
NameError: name 'a' is not defined

Could this be a bug in Graal Python?

[ppisl]

Thanks for reporting this. I'm going to fix it. This issue is cased by new parser that was integrated last week. You can use switch --python.UseExperimentalParser=false to use original parser. We are going to keep both parsers for a while.

[oroppas]

Hi @ppisl,

Thanks for the info. I'll be waiting for the fix for the new parser. Meanwhile, I tried to revert to the old parser without success:

$ graalpython --experimental-options --python.UseExperimentalParser=false ./test.py 
Please note: This Python implementation is in the very early stages, and can run little more than basic benchmarks at this point.
mkl , , openblas, blis, 
Traceback (most recent call last):
  File "/run/media/ryutas/fba67dee-3fe6-4f11-980a-3e50e9a564c5/Ryuta_Data/graalpython/list_comprehension/test.py", line 3, in <module 'test.py'>
    print([b for b in [a.strip() for a in libs.split(',')] if b])
NameError: name 'a' is not defined

Can you verify this behavior?

[ppisl]

Hi @oroppas,

you are right. It looks like that the parser properties are not propagated to the native image correctly. But when you run in jvm mode, then it works. So you can use:

$ graalpython --jvm --experimental-options --python.UseExperimentalParser=false ./test.py

I have already the fix for this issue, just waiting for merging this.

[ppisl]

So the fix is now pushed. I will close the bug, when I will have rights. So far I can not even assign the issue to me. Thanks

[oroppas]

I can confirm the fix. Thanks!

[linl33]

A similar issue is still present in version 20.3.0. Graal throws a NameError when the nested comprehension is a generator.

>>> [e for e in (s.strip() for s in '1 2 3'.split(' '))]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 's' is not defined

>>> [e for e in [s.strip() for s in '1 2 3'.split(' ')]]
['1', '2', '3']

CPython

>>> [e for e in (s.strip() for s in '1 2 3'.split(' '))]
['1', '2', '3']

[msimacek]

I can reproduce that, thank you for the report. @ppisl would you mind taking a look?

[ppisl]

I am working on this and I have found the problem and fix. Should be propageted here soon.