Hi, Guido van Rossum wrote:

On Tue, May 27, 2008 at 9:47 AM, Stefan Behnel wrote:

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Could this function get a public interface? I do not think Cython is the only case where C code wants to modify a type after its creation, and copying the code over seems like a hack to me.

I'm fine with giving it a public interface. Please submit a patch with docs included.

Straight forward patch is attached (against 3.0a5). Works for me in Cython. I thought about a name like "Taint(t)" or "ClearTypeCache(t)", but then went with the coward solution of calling the function PyType_Modified() as it was (almost) named internally. BTW, I noticed that the code in typeobject.c uses "DECREF before set" two times, like this: method_cache[h].version = type->tp_version_tag; method_cache[h].value = res; /* borrowed */ Py_INCREF(name); Py_DECREF(method_cache[h].name); method_cache[h].name = name; During the call to Py_DECREF, the cache content is incorrect, so can't this run into the same problem that Py_CLEAR() aims to solve? I attached a patch for that, too, just in case. Stefan

Stefan Behnel schrieb:

Straight forward patch is attached (against 3.0a5). Works for me in Cython. I thought about a name like "Taint(t)" or "ClearTypeCache(t)", but then went with the coward solution of calling the function PyType_Modified() as it was (almost) named internally.

BTW, I noticed that the code in typeobject.c uses "DECREF before set" two times, like this:

method_cache[h].version = type->tp_version_tag; method_cache[h].value = res; /* borrowed */ Py_INCREF(name); Py_DECREF(method_cache[h].name); method_cache[h].name = name;

During the call to Py_DECREF, the cache content is incorrect, so can't this run into the same problem that Py_CLEAR() aims to solve? I attached a patch for that, too, just in case.

Please create two tickets in the bug tracker and append the patches. Christian

Antoine Pitrou wrote:

Stefan Behnel writes:

...

BTW, I noticed that the code in typeobject.c uses "DECREF before set" two times, like this:

method_cache[h].version = type->tp_version_tag; method_cache[h].value = res; /* borrowed */ Py_INCREF(name); Py_DECREF(method_cache[h].name); method_cache[h].name = name;

Since this is so common, would it be useful to define a macro for the correct construct?

Something like

#define Py_SETREF(var, obj) \ { PyObject *tmp = (var); Py_INCREF(obj); \ (var) = (obj); Py_XDECREF(tmp); }

Or, if we want to allow more optimizations, make two versions of it:

#define Py_SETREF(var, obj) \ { PyObject *tmp = (var); Py_INCREF(obj); \ (var) = (obj); Py_DECREF(tmp); }

#define Py_XSETREF(var, obj) \ { PyObject *tmp = (var); Py_INCREF(obj); \ (var) = (obj); Py_XDECREF(tmp); }

Both sound like a good idea to me. Having to think about whether or not DECREF poses a problem in a specific case is just cumbersome. Stefan