GSoC Week #1

The first coding week of Google Summer of Code is just past. I was working on some bug fixes for Cython, according to the schedule in my proposal.

The first thing I did is revised a patch I produced during the GSoC application period for Cython Ticket #422 (bug in setting __module__). With some suggestion provided by Robert,  I found a way to make the module name as a const string by using a mechanism already provided by Cython, then there’s no need for conversion between PyObject and C string.

After that, I came to the nonlocal keyword, which is a Python 3 feature specified by PEP 3104. Implementation is straightforward – modify the parser, add a new node that lookup the name so it bring the variable from outer closure scope to the current scope. Since the ‘nonlocal’ keyword is similar to the ‘global’ keyword, so I can have the ‘global’ as a model to follow during implementing this. However, then I found the type inferencer did something wrong on the variables declared nonlocal, so I disable it on nonlocal variables. Now the test case runs, but refnanny starts to complain, since now inner functions can change the object that an outer name pointed to, and this will confuse refnanny. To silence refnanny, I fixed the refnanny-generating code to completely pull the closure variables out of refnanny’s control. Then it is done. With some more tests, I also discovered a new bug in the closure code.

Then I worked out the ‘with’ statement with multiple manages. This is easier.  What I did is just a bit refactoring of the parser code for with statement.

I also looked into a ticket saying the Python 3 integer division is not respected by C ints. However, when I try to reproduce the described erroneous behavior,  I found this seems already get fixed. So I just produced a test case for it.

Finally, I got the explicit exception chaining syntax done.  Again, this involves changes in parser, node and some utility code. It just spend some time to write the test case that runs simultaneously on both Python 2 and 3.

With these work, I think I have grabbed the basic idea of how the parser, tree node and scoping works in Cython. The next challenge would be to figure out how the Cython “-3” option should change the behavior.


June 1, 2010. Uncategorized.

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