[Cython] [cython-users] Cython .pxd introspection: listing defined constants

W. Trevor King wking at drexel.edu
Tue Feb 22 21:02:08 CET 2011

On Tue, Feb 22, 2011 at 08:18:21PM +0100, Stefan Behnel wrote:
> W. Trevor King, 22.02.2011 18:55:
> > I've been working on a more explicit parser that removes the ambiguity
> > behind the various visibilities.  This will help me ensure proper
> > impolementation of my cdef-ed enums/structs/..., and make it easier to
> > update visibility syntax in the future.  Take a look and let me know
> > if you think this is a useful direction to take:
> First thing that caught my eyes: I hope you do not intend to leave the 
> logging usage in the parser. This is seriously performance critical code 
> that Cython compiles down to pretty fast C code. Note that you can use a 
> debugger and Python's profiling/tracing interface to find out what's 
> happening, without code impact.

I can strip them out afterwards, but it helps me figure out what I've
broken if I shift too much around at the same time.

I don't know enough about Python's trace module to know if I can turn
on tracing only for functions defined in a single module or not, since
otherwise its hard for me to separate signal from noise.

> Some of the log statements span more than one line, which makes it trickier 
> to strip them out with sed&friends (but backing out the initial changeset 
> would likely make it simple enough to remove the rest manually).

Hmm, perhaps I'll condense the logging statements down onto one (long)
line a piece, that will make it easy to comment/uncomment them with
sed/emacs/etc.  I suppose once Cython can compile the logging module
we could leave them in with reduced overhead ;).

> Also note that it's best to write runnable tests ("tests/run/"). The
> tests in "tests/compile/" are only compiled and imported. See the
> hacking guide in the wiki. I know you're not there yet with your
> implementation, I'm just mentioning it.

Thanks for the tip.

> CtxAttribute is the wrong name, though.  And the class copy
> implementation gets even more generic than it already was in the
> Ctx. I'm not a big fan of that, especially not in the parser. For
> one, it prevents changing the classes into cdef classes, which had
> long been on my list for Ctx.

An easy, if uglier, workaround would be to prepend attributes with the
class name, e.g. CBinding.visibility -> CBinding.c_binding_visiblity.
Then the Ctx class could subclass the current CtxAttribute classes
instead of binding instances of each of them.  That way Ctx would keep
its traditional flat attribute namespace and easy deepcopy, but
eveyone in Nodes, etc. that will use the attributes would become
class-name dependent.

The CtxAttribute class is, as its docstring says, just a hook for its
deepcopy method.  With an alternative deepcopy implementation,
CtxAttribute could be replaced with the standard `object`, so don't
worry too much about its name at this point ;).

> CSource: doesn't sound like quite the right name - it does not describe a C 
> source file but information that Cython has about non-Cython things.

It's a container for attributes that describe the presence and
location of backing C definitions.

* cdef: "Will there be a backing C defintion?
* extern: "Has someone else already written it?"
* name/namespace: "What did they call it?"

If you'd rather I called the class something else, I'm certainly
willing to change it.

> I also doubt that Cython allows you to call an attribute "cdef", you'll 
> need to change that.

It seems to work for me:
  >>> import Cython.Compiler.Parsing as P
  >>> P.__file__
  >>> c = P.CSource()
  >>> dir(c)
  [..., 'cdef', 'deepcopy', 'extern', 'name', 'namespace']
  >>> c.cdef
  >>> c.cdef = 1
  >>> c.cdef

However, I agree that it's generally a bad idea to play around with
keywords.  I'll revert it to the wordier-but-less-confusing

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