通过 subprocess.check_output 调用的可执行文件在控制台上打印，但不返回结果

Question

在 Windows 机器上，我尝试从 Python 调用外部可执行文件并收集其输出以进行进一步处理。因为在调用可执行文件之前必须设置一个本地路径变量，所以我创建了一个批处理脚本，

• 首先调用另一个脚本来设置%PATH% 和
• 然后使用给定的参数调用可执行文件。

*.bat 文件如下所示：

@echo off
call set_path.bat
@echo on
executable.exe %*

Python 代码如下：

print("before call");
result = subprocess.check_output([batfile, parameters], stderr=subprocess.STDOUT, shell=True);
print("after call");

print("------- ------- ------- printing result ------- ------- ------- ");
print(result);
print("------- ------- ------- /printing result ------- ------- ------- ");

现在，从技术上讲，这是可行的。使用预期的参数调用可执行文件，运行，完成并产生结果。我知道这一点，因为它们在运行 Python 脚本的控制台中被嘲弄地显示。

但是，结果字符串只包含批处理脚本返回的内容，而不是可执行文件的输出：

通话前

喂？是的，这是executable.exe

通话后

------- ------- -------- 打印结果 ------- ------- -------

C:\Users\me\Documents\pythonscript\execute\executable.exe "para1|para2|para3"

------- ------- ------- /打印结果 ------- ------- -------

subprocess.check_output 命令本身以某种方式将预期的输出打印到控制台，它返回的内容仅包含@echo 再次打开后的批处理文件的输出。

如何访问可执行文件的输出并将其保存为字符串以便进一步工作？

或者我是否必须以某种方式修改批处理文件以捕获并打印输出，以便它最终会出现在 check_output 的结果中？如果是这样，我该怎么做？

Answer 1

如果程序直接写入控制台（例如通过打开CONOUT$ 设备）而不是进程标准句柄，则唯一的选择是直接读取控制台屏幕缓冲区。为了使这更简单，从一个新的空屏幕缓冲区开始。通过以下函数创建、调整大小、初始化和激活新的屏幕缓冲区：

• CreateConsoleScreenBuffer
• GetConsoleScreenBufferInfoEx（最低支持客户端：Windows Vista）
• SetConsoleScreenBufferInfoEx（最低支持客户端：Windows Vista）
• SetConsoleWindowInfo
• FillConsoleOutputCharacter
• SetConsoleActiveScreenBuffer

确保在调用CreateConsoleScreenBuffer 时请求GENERIC_READ | GENERIC_WRITE 访问权限。稍后您需要读取权限才能读取屏幕内容。

专门针对 Python，使用 ctypes 调用 Windows 控制台 API 中的函数。此外，如果您通过msvcrt.open_osfhandle 使用C 文件描述符包装句柄，那么您可以将其作为subprocess.Popen 的stdout 或stderr 参数传递。

屏幕缓冲区的文件描述符或句柄无法通过read、ReadFile 甚至ReadConsole 直接读取。如果您有文件描述符，请通过msvcrt.get_osfhandle 获取底层句柄。给定一个屏幕缓冲区句柄，调用ReadConsoleOutputCharacter 从屏幕读取。下面示例代码中的read_screen 函数演示了从屏幕缓冲区开始到光标位置的读取。

需要将进程附加到控制台才能使用控制台 API。为此，我包含了一个简单的allocate_console 上下文管理器来临时打开一个控制台。这在通常不附加到控制台的 GUI 应用程序中很有用。

以下示例在 Windows 7 和 10、Python 2.7 和 3.5 中进行了测试。

ctypes 定义

import os
import contextlib
import msvcrt
import ctypes
from ctypes import wintypes

kernel32 = ctypes.WinDLL('kernel32', use_last_error=True)

GENERIC_READ  = 0x80000000
GENERIC_WRITE = 0x40000000
FILE_SHARE_READ  = 1
FILE_SHARE_WRITE = 2
CONSOLE_TEXTMODE_BUFFER = 1
INVALID_HANDLE_VALUE = wintypes.HANDLE(-1).value
STD_OUTPUT_HANDLE = wintypes.DWORD(-11)
STD_ERROR_HANDLE = wintypes.DWORD(-12)

def _check_zero(result, func, args):
    if not result:
        raise ctypes.WinError(ctypes.get_last_error())
    return args

def _check_invalid(result, func, args):
    if result == INVALID_HANDLE_VALUE:
        raise ctypes.WinError(ctypes.get_last_error())
    return args

if not hasattr(wintypes, 'LPDWORD'): # Python 2
    wintypes.LPDWORD = ctypes.POINTER(wintypes.DWORD)
    wintypes.PSMALL_RECT = ctypes.POINTER(wintypes.SMALL_RECT)

class COORD(ctypes.Structure):
    _fields_ = (('X', wintypes.SHORT),
                ('Y', wintypes.SHORT))

class CONSOLE_SCREEN_BUFFER_INFOEX(ctypes.Structure):
    _fields_ = (('cbSize',               wintypes.ULONG),
                ('dwSize',               COORD),
                ('dwCursorPosition',     COORD),
                ('wAttributes',          wintypes.WORD),
                ('srWindow',             wintypes.SMALL_RECT),
                ('dwMaximumWindowSize',  COORD),
                ('wPopupAttributes',     wintypes.WORD),
                ('bFullscreenSupported', wintypes.BOOL),
                ('ColorTable',           wintypes.DWORD * 16))
    def __init__(self, *args, **kwds):
        super(CONSOLE_SCREEN_BUFFER_INFOEX, self).__init__(
                *args, **kwds)
        self.cbSize = ctypes.sizeof(self)

PCONSOLE_SCREEN_BUFFER_INFOEX = ctypes.POINTER(
                                    CONSOLE_SCREEN_BUFFER_INFOEX)
LPSECURITY_ATTRIBUTES = wintypes.LPVOID

kernel32.GetStdHandle.errcheck = _check_invalid
kernel32.GetStdHandle.restype = wintypes.HANDLE
kernel32.GetStdHandle.argtypes = (
    wintypes.DWORD,) # _In_ nStdHandle

kernel32.CreateConsoleScreenBuffer.errcheck = _check_invalid
kernel32.CreateConsoleScreenBuffer.restype = wintypes.HANDLE
kernel32.CreateConsoleScreenBuffer.argtypes = (
    wintypes.DWORD,        # _In_       dwDesiredAccess
    wintypes.DWORD,        # _In_       dwShareMode
    LPSECURITY_ATTRIBUTES, # _In_opt_   lpSecurityAttributes
    wintypes.DWORD,        # _In_       dwFlags
    wintypes.LPVOID)       # _Reserved_ lpScreenBufferData

kernel32.GetConsoleScreenBufferInfoEx.errcheck = _check_zero
kernel32.GetConsoleScreenBufferInfoEx.argtypes = (
    wintypes.HANDLE,               # _In_  hConsoleOutput
    PCONSOLE_SCREEN_BUFFER_INFOEX) # _Out_ lpConsoleScreenBufferInfo

kernel32.SetConsoleScreenBufferInfoEx.errcheck = _check_zero
kernel32.SetConsoleScreenBufferInfoEx.argtypes = (
    wintypes.HANDLE,               # _In_  hConsoleOutput
    PCONSOLE_SCREEN_BUFFER_INFOEX) # _In_  lpConsoleScreenBufferInfo

kernel32.SetConsoleWindowInfo.errcheck = _check_zero
kernel32.SetConsoleWindowInfo.argtypes = (
    wintypes.HANDLE,      # _In_ hConsoleOutput
    wintypes.BOOL,        # _In_ bAbsolute
    wintypes.PSMALL_RECT) # _In_ lpConsoleWindow

kernel32.FillConsoleOutputCharacterW.errcheck = _check_zero
kernel32.FillConsoleOutputCharacterW.argtypes = (
    wintypes.HANDLE,  # _In_  hConsoleOutput
    wintypes.WCHAR,   # _In_  cCharacter
    wintypes.DWORD,   # _In_  nLength
    COORD,            # _In_  dwWriteCoord
    wintypes.LPDWORD) # _Out_ lpNumberOfCharsWritten

kernel32.ReadConsoleOutputCharacterW.errcheck = _check_zero
kernel32.ReadConsoleOutputCharacterW.argtypes = (
    wintypes.HANDLE,  # _In_  hConsoleOutput
    wintypes.LPWSTR,  # _Out_ lpCharacter
    wintypes.DWORD,   # _In_  nLength
    COORD,            # _In_  dwReadCoord
    wintypes.LPDWORD) # _Out_ lpNumberOfCharsRead

功能

@contextlib.contextmanager
def allocate_console():
    allocated = kernel32.AllocConsole()
    try:
        yield allocated
    finally:
        if allocated:
            kernel32.FreeConsole()

@contextlib.contextmanager
def console_screen(ncols=None, nrows=None):
    info = CONSOLE_SCREEN_BUFFER_INFOEX()
    new_info = CONSOLE_SCREEN_BUFFER_INFOEX()
    nwritten = (wintypes.DWORD * 1)()
    hStdOut = kernel32.GetStdHandle(STD_OUTPUT_HANDLE)
    kernel32.GetConsoleScreenBufferInfoEx(
           hStdOut, ctypes.byref(info))
    if ncols is None:
        ncols = info.dwSize.X
    if nrows is None:
        nrows = info.dwSize.Y
    elif nrows > 9999:
        raise ValueError('nrows must be 9999 or less')
    fd_screen = None
    hScreen = kernel32.CreateConsoleScreenBuffer(
                GENERIC_READ | GENERIC_WRITE,
                FILE_SHARE_READ | FILE_SHARE_WRITE,
                None, CONSOLE_TEXTMODE_BUFFER, None)
    try:
        fd_screen = msvcrt.open_osfhandle(
                        hScreen, os.O_RDWR | os.O_BINARY)
        kernel32.GetConsoleScreenBufferInfoEx(
               hScreen, ctypes.byref(new_info))
        new_info.dwSize = COORD(ncols, nrows)
        new_info.srWindow = wintypes.SMALL_RECT(
                Left=0, Top=0, Right=(ncols - 1),
                Bottom=(info.srWindow.Bottom - info.srWindow.Top))
        kernel32.SetConsoleScreenBufferInfoEx(
                hScreen, ctypes.byref(new_info))
        kernel32.SetConsoleWindowInfo(hScreen, True,
                ctypes.byref(new_info.srWindow))
        kernel32.FillConsoleOutputCharacterW(
                hScreen, u'\0', ncols * nrows, COORD(0,0), nwritten)
        kernel32.SetConsoleActiveScreenBuffer(hScreen)
        try:
            yield fd_screen
        finally:
            kernel32.SetConsoleScreenBufferInfoEx(
                hStdOut, ctypes.byref(info))
            kernel32.SetConsoleWindowInfo(hStdOut, True,
                    ctypes.byref(info.srWindow))
            kernel32.SetConsoleActiveScreenBuffer(hStdOut)
    finally:
        if fd_screen is not None:
            os.close(fd_screen)
        else:
            kernel32.CloseHandle(hScreen)

def read_screen(fd):
    hScreen = msvcrt.get_osfhandle(fd)
    csbi = CONSOLE_SCREEN_BUFFER_INFOEX()
    kernel32.GetConsoleScreenBufferInfoEx(
        hScreen, ctypes.byref(csbi))
    ncols = csbi.dwSize.X
    pos = csbi.dwCursorPosition
    length = ncols * pos.Y + pos.X + 1
    buf = (ctypes.c_wchar * length)()
    n = (wintypes.DWORD * 1)()
    kernel32.ReadConsoleOutputCharacterW(
        hScreen, buf, length, COORD(0,0), n)
    lines = [buf[i:i+ncols].rstrip(u'\0')
                for i in range(0, n[0], ncols)]
    return u'\n'.join(lines)

示例

if __name__ == '__main__':
    import io
    import textwrap
    import subprocess

    text = textwrap.dedent('''\
        Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do
        eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut
        enim ad minim veniam, quis nostrud exercitation ullamco laboris
        nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor
        in reprehenderit in voluptate velit esse cillum dolore eu
        fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
        proident, sunt in culpa qui officia deserunt mollit anim id est
        laborum.''')

    cmd = ("python -c \""
           "print('piped output');"
           "conout = open(r'CONOUT$', 'w');"
           "conout.write('''%s''')\"" % text)

    with allocate_console() as allocated:
        with console_screen(nrows=1000) as fd_conout:
            stdout = subprocess.check_output(cmd).decode()
            conout = read_screen(fd_conout)
            with io.open('result.txt', 'w', encoding='utf-8') as f:
                f.write(u'stdout:\n' + stdout)
                f.write(u'\nconout:\n' + conout)

输出

stdout:
piped output

conout:
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do
eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut
enim ad minim veniam, quis nostrud exercitation ullamco laboris
nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor
in reprehenderit in voluptate velit esse cillum dolore eu
fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
proident, sunt in culpa qui officia deserunt mollit anim id est
laborum.