[英]Python C-API access String constants
I wanted to implement a library I have written for python in C using the C-API of python. 我想使用python的C-API实现我在C中为python编写的库。 In python I can declare "constants" in my module by just stating: 在python中,我可以通过声明:在我的模块中声明“常量”:
RED = "red" # Not really a constant, I know
BLUE = "blue" # but suitable, nevertheless
def solve(img_h):
# Awesome computations
return (RED, BLUE)[some_flag]
Those constants are then later returned by the functions offered by the module. 然后,这些常量将由模块提供的函数返回。 I have some trouble doing the same thing in C. Here is what I got so far: 我在C中做同样的事情有些麻烦。这是我到目前为止所得到的:
PyMODINIT_FUNC
PyInit_puzzler(void)
{
PyObject* module = PyModule_Create(&Module);
(void) PyModule_AddStringConstant(module, "BLUE", "blue");
(void) PyModule_AddStringConstant(module, "RED", "red");
return module;
}
PyObject* solve(PyObject* module, PyObject* file_handle)
{
// Do some awesome computations based on the file
// Involves HUGE amounts of memory management, thus efficient in C
// PROBLEM: How do I return the StringConstants from here?
return some_flag ? BLUE : RED;
}
I have already marked the problematic part. 我已经标出了有问题的部分。 After I add string constants to the module with PyModule_AddStringConstant(module, "FOO", "foo");
在我使用PyModule_AddStringConstant(module, "FOO", "foo");
向模块添加字符串常量后PyModule_AddStringConstant(module, "FOO", "foo");
how can I actually return them as a PyObject*
from my methods? 我怎样才能从我的方法中将它们作为PyObject*
实际返回? Do I need to increase the ref-counter when I return them? 我退货时是否需要增加参考柜台?
Since PyModule_AddStringConstant(module, name, value) adds the constant to the module, it should be available from the module's dictionary which can be acquired with PyModule_GetDict(module) . 由于PyModule_AddStringConstant(模块,名称,值)将常量添加到模块,因此它应该可以从模块的字典中获得,该字典可以使用PyModule_GetDict(模块)获取。 You can then access any attribute from the module via its dictionary using PyDict_GetItemString(dict, key) This is how you can access the constants from your module (after their definitions): 然后,您可以使用PyDict_GetItemString(dict,key)通过其字典访问模块中的任何属性。这是您可以从模块中访问常量的方法(在它们的定义之后):
// Get module dict. This is a borrowed reference.
PyObject* module_dict = PyModule_GetDict(module);
// Get BLUE constant. This is a borrowed reference.
PyObject* BLUE = PyDict_GetItemString(module_dict, "BLUE");
// Get RED constant. This is a borrowed reference.
PyObject* RED = PyDict_GetItemString(module_dict, "RED");
To put this into context with your solve()
function, you want something similar to: 要使用solve()
函数将其置于上下文中,您需要类似于:
PyObject* solve(PyObject* module, PyObject* file_handle)
{
// Do some awesome computations based on the file
// Involves HUGE amounts of memory management, thus efficient in C
// Return string constant at the end.
PyObject* module_dict = PyModule_GetDict(module);
PyObject* constant = NULL;
if (some_flag) {
// Return BLUE constant. Since BLUE is a borrowed
// reference, increment its reference count before
// returning it.
constant = PyDict_GetItemString(module_dict, "BLUE");
Py_INCREF(constant);
} else {
// Return RED constant. Since RED is a borrowed
// reference, increment its reference count before
// returning it.
constant = PyDict_GetItemString(module_dict, "RED");
Py_INCREF(constant);
}
// NOTE: Before you return, make sure to release any owned
// references that this function acquired. `module_dict` does
// not need to be released because it is merely "borrowed".
// Return the constant (either BLUE or RED) as an owned
// reference. Whatever calls `solve()` must make sure to
// release the returned reference with `Py_DECREF()`.
return constant;
}
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