转换POSIX->WIN路径，在Cygwin Python中，不调用cygpath

Question

我使用在Python的Cygwin版本中运行的Python脚本来创建向本机Windows实用程序(不支持Cygwin)发出的命令。这需要在发出命令之前将路径参数从POSIX转换为WIN格式。

调用cygpath实用程序是最好的方式，因为它使用Cygwin来做它应该做的事情，但它也有点可怕(而且很慢)。

我已经在运行Python的Cygwin版本了--所以提供了进行转换的代码。似乎应该有一个Cygwin/Python特定的扩展，让我可以直接在Python中使用这个功能，而不必启动一个全新的进程。

Answer 1

这可以通过使用ctype调用Cygwin API来实现。以下代码适用于我-我在Windows 2012上使用64位cygwin DLL版本2.5.2，这适用于Python 2.7.10和Python 3.4.3的Cygwin版本。

基本上，我们从cygwin1.dll调用cygwin_create_path来执行路径转换。该函数分配包含已转换路径的内存缓冲区(使用malloc)。因此，我们需要从cygwin1.dll使用free来释放它分配的缓冲区。

请注意，下面的xunicode是six (Python2/3兼容性库)的替代方案；如果您需要同时支持Python2和Python3，six是更好的答案，但我希望我的示例不依赖于任何非捆绑模块，这就是为什么我这样做的原因。

from ctypes import cdll, c_void_p, c_int32, cast, c_char_p, c_wchar_p
from sys import version_info

xunicode = str if version_info[0] > 2 else eval("unicode")

# If running under Cygwin Python, just use DLL name
# If running under non-Cygwin Windows Python, use full path to cygwin1.dll
# Note Python and cygwin1.dll must match bitness (i.e. 32-bit Python must
# use 32-bit cygwin1.dll, 64-bit Python must use 64-bit cygwin1.dll.)
cygwin = cdll.LoadLibrary("cygwin1.dll")
cygwin_create_path = cygwin.cygwin_create_path
cygwin_create_path.restype = c_void_p
cygwin_create_path.argtypes = [c_int32, c_void_p]

# Initialise the cygwin DLL. This step should only be done if using
# non-Cygwin Python. If you are using Cygwin Python don't do this because
# it has already been done for you.
cygwin_dll_init = cygwin.cygwin_dll_init
cygwin_dll_init.restype = None
cygwin_dll_init.argtypes = []
cygwin_dll_init()

free = cygwin.free
free.restype = None
free.argtypes = [c_void_p]

CCP_POSIX_TO_WIN_A = 0
CCP_POSIX_TO_WIN_W = 1
CCP_WIN_A_TO_POSIX = 2
CCP_WIN_W_TO_POSIX = 3

def win2posix(path):
    """Convert a Windows path to a Cygwin path"""
    result = cygwin_create_path(CCP_WIN_W_TO_POSIX,xunicode(path))
    if result is None:
        raise Exception("cygwin_create_path failed")
    value = cast(result,c_char_p).value
    free(result)
    return value

def posix2win(path):
    """Convert a Cygwin path to a Windows path"""
    result = cygwin_create_path(CCP_POSIX_TO_WIN_W,str(path))
    if result is None:
        raise Exception("cygwin_create_path failed")
    value = cast(result,c_wchar_p).value
    free(result)
    return value

# Example, convert LOCALAPPDATA to cygwin path and back
from os import environ
localAppData = environ["LOCALAPPDATA"]
print("Original Win32 path: %s" % localAppData)
localAppData = win2posix(localAppData)
print("As a POSIX path: %s" % localAppData)
localAppData = posix2win(localAppData)
print("Back to a Windows path: %s" % localAppData)

Answer 2

从浏览cygpath source来看，cygpath似乎有一个不平凡的实现，并且没有提供任何库版本。

cygpath支持使用-f选项从文件中获取输入(或使用-f -从标准输入中获取输入)，并且可以采用多个路径，每次都会生成一个转换后的路径，因此您可能会创建一个打开的cygpath实例(使用Python的subprocess.Popen)，而不是每次都重新启动cygpath。

Answer 3

我宁愿写这个使用cygwin动态链接库的Python helper：

import errno
import ctypes
import enum
import sys

class ccp_what(enum.Enum):
    posix_to_win_a = 0 # from is char *posix, to is char *win32
    posix_to_win_w = 1 # from is char *posix, to is wchar_t *win32
    win_a_to_posix = 2 # from is char *win32, to is char *posix
    win_w_to_posix = 3 # from is wchar_t *win32, to is char *posix

    convtype_mask = 3

    absolute = 0          # Request absolute path (default).
    relative = 0x100      # Request to keep path relative.
    proc_cygdrive = 0x200 # Request to return /proc/cygdrive path (only with CCP_*_TO_POSIX)

class CygpathError(Exception):
    def __init__(self, errno, msg=""):
        self.errno = errno
        super(Exception, self).__init__(os.strerror(errno))

class Cygpath(object):
    bufsize = 512

    def __init__(self):
        if 'cygwin' not in sys.platform:
            raise SystemError('Not running on cygwin')

        self._dll = ctypes.cdll.LoadLibrary("cygwin1.dll")

    def _cygwin_conv_path(self, what, path, size = None):
        if size is None:
            size = self.bufsize
        out = ctypes.create_string_buffer(size)
        ret = self._dll.cygwin_conv_path(what, path, out, size)
        if ret < 0:
            raise CygpathError(ctypes.get_errno())
        return out.value

    def posix2win(self, path, relative=False):
        out = ctypes.create_string_buffer(self.bufsize)
        t = ccp_what.relative.value if relative else ccp_what.absolute.value
        what = ccp_what.posix_to_win_a.value | t
        return self._cygwin_conv_path(what, path)

    def win2posix(self, path, relative=False):
        out = ctypes.create_string_buffer(self.bufsize)
        t = ccp_what.relative.value if relative else ccp_what.absolute.value
        what = ccp_what.win_a_to_posix.value | t
        return self._cygwin_conv_path(what, path)