在python 2.7 ctypes中构建UCS4字符串缓冲区 [英] Building an UCS4 string buffer in python 2.7 ctypes

问题描述

试图重新创建 _winapi.c 的 getenvironment（..） C函数（直接链接）在纯python中使用 ctypes ，我想知道如何翻译以下C代码：

In an attempt to recreate the getenvironment(..) C function of _winapi.c (direct link) in plain python using ctypes, I'm wondering how the following C code could be translated:

buffer = PyMem_NEW(Py_UCS4, totalsize);
if (! buffer) {
    PyErr_NoMemory();
    goto error;
}
p = buffer;
end = buffer + totalsize;

for (i = 0; i < envsize; i++) {
    PyObject* key = PyList_GET_ITEM(keys, i);
    PyObject* value = PyList_GET_ITEM(values, i);
    if (!PyUnicode_AsUCS4(key, p, end - p, 0))
        goto error;
    p += PyUnicode_GET_LENGTH(key);
    *p++ = '=';
    if (!PyUnicode_AsUCS4(value, p, end - p, 0))
        goto error;
    p += PyUnicode_GET_LENGTH(value);
    *p++ = '\0';
}

/* add trailing null byte */
*p++ = '\0';

似乎函数 ctypes.create_unicode_buffer（..）（ doc ，代码）正在做的很接近，我可以重现如果只有我可以访问 Py_UCS4 C类型，或者确保它链接到通过 ctypes 。

It seems that the function ctypes.create_unicode_buffer(..) (doc, code) is doing something quite close that I could reproduce if only I could have an access to Py_UCS4 C type or be sure of its link to any other type accessible to python through ctypes.

c_wchar 会是一个很好的候选人吗？但看来我无法做出这样的假设，因为如果我正确的话，Python 2.7可以在 UCS-2 中进行编译（源代码），我想Windows真的在等待 UCS-4 ……即使看起来 ctypes.wintypes.LPWSTR 是 c_wchart_p （代码）。

Would c_wchar be a good candidate ?, but it seems I can't make that assumption, as python 2.7 could be compiled in UCS-2 if I'm right (source), and I guess windows is really waiting fo UCS-4 there... even if it seems that ctypes.wintypes.LPWSTR is an alias to c_wchart_p in cPython 2.7 (code).

对于这个问题，可以假设目标平台是Windows上的python 2.7（如果有帮助）。

For this question, it is safe to make the assumption that the target platform is python 2.7 on Windows if that helps.

上下文（如果有重要意义）：

Context (if it has some importance):

我正在研究第一个在 ctypes 中尝试对cPython 2.7的bug进行普通的python修复，击中Windows subprocess.Popen（..）实施。 此错误无法修复。此错误阻止在命令行调用中使用unicode（作为可执行文件名称或自变量）。这在python 3中已修复，所以我要在纯Python中反向实现所需的 CreateProcess（..）中的实际cPython3实现。 c> _winapi.c 依次调用 getenvironment（..）。
在与相关的问题的此答案的注释中提到了这种可能的解决方法。 subprocess.Popen（..） unicode问题。

I'm in the process of delving for the first time in ctypes to attempt a plain python fix at cPython 2.7's bug hitting windows subprocess.Popen(..) implementation. This bug is a won't fix. This bug prevents the usage of unicode in command line calls (as executable name or arguments). This is fixed in python 3, so I'm having a go at reverse implementing in plain python the actual cPython3 implementation of the required CreateProcess(..) in _winapi.c which calls in turn getenvironment(..). This possible workaround was mentionned in the comments of this answer to a question related to subprocess.Popen(..) unicode issues.

推荐答案

关于构建的标题，特别是 UCS4 缓冲区。但是它以粗体部分回答了这个问题，并设法创建了一个unicode缓冲区，该缓冲区似乎可以在Windows上的当前python 2.7上运行：（所以也许不需要UCS4）。

This doesn't answer the part in the title about build specifically UCS4 buffer. But it gives a partial answer to the question in bold and manage to create a unicode buffer that seems to work on my current python 2.7 on windows: (so maybe UCS4 is not required).

所以我们在这里假设 c_wchar 是Windows所需的（对我来说还不是很清楚，如果是UCS4或UCS2，它可能没有重要性，但我想对自己的知识抱有非常轻的信心。）

So we are here taking the assumption that c_wchar is what windows require (if it is UCS4 or UCS2 is not so clear to me yet, and it might have no importance, but I recon having a very light confidence in my knowledge here).

因此，这是可按问题要求复制C代码的python代码：

So here is the python code that reproduces the C code as requested in the question:

## creation of buffer of size totalsize
wenv = (c_wchar * totalsize)()    
wenv.value = (unicode("").join([
    unicode("%s=%s\0") % (key, value)
    for k, v in env.items()])) + "\0"

此 wenv CreateProcessW ，这似乎可行。

This wenv can then be fed to CreateProcessW and this seems to work.

这篇关于在python 2.7 ctypes中构建UCS4字符串缓冲区的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！