C API type issue
Gabriel Genellina
gagsl-py2 at yahoo.com.ar
Fri Oct 3 16:22:15 EDT 2008
En Fri, 03 Oct 2008 12:27:50 -0300, Rich Henry <againstmethod at gmail.com>
escribió:
> Made a simple little test program as im learning to embed python, have a
> simple script that just sets x=10.0 in test.py and prints type(x). Python
> prints that x is a float but PyFloat_Check() returns false. If i removed
> the
> check and just force it to print the double value, its correct. Any ideas
> why PyFloat_Check() returns false on a float? Thanks in advance.
You got the reference count wrong. This is by far the most common source
of errors when writting C code for Python (at least for beginners)
> #include "Python.h"
> #include <cstdio>
>
> int main(int argc, char** argv)
> {
> FILE* fp = fopen("test.py", "r");
> assert(fp);
>
> Py_Initialize();
>
> //
> // create a dictionary, load the builtins and execute our file
> //
> PyObject *d = PyDict_New();
> assert(d);
> PyDict_SetItemString(d, "__builtins__", PyEval_GetBuiltins());
> PyRun_File(fp, "test.py", Py_file_input, d, NULL);
Instead of a bare dictionary, I'd use a module. Or the __main__ module.
See how PyRun_SimpleFileExFlags handles this (or just use that function,
or other variant).
> //
> // get a variable that should be in our global namespace
> //
> PyObject *x = PyDict_GetItemString(d, "x");
> assert(x);
This returns a borrowed reference, not a new one.
> Py_DECREF(d);
This releases the only reference to d, and the dictionary is deleted. This
in turn releases the last refrence to x, and it's deleted too.
> // determine its type and print it
> //
> if(PyFloat_Check(x))
> {
> printf("x = %lf\n", PyFloat_AS_DOUBLE(x));
> }
At this stage x is an invalid object.
> Py_DECREF(x);
And this is wrong now.
>
> Py_Finalize();
> fclose(fp);
> return 0;
> }
--
Gabriel Genellina
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