python - 如何在 Windows 中重定向 Python 中的 C 级流？

Question

Eli Bendersky 已经彻底解释了如何“Redirecting all kinds of stdout in Python”，特别是重定向 C 级流，例如共享库 (dll) 的标准输出。但是这个例子是在linux下，在windows下不行，主要是以下几行:

libc = ctypes.CDLL(None)
c_stdout = ctypes.c_void_p.in_dll(libc = ctypes.CDLL(None), 'stdout')

我们如何让它在 Windows 中工作？

Answer 1

我在 Drekin's code 中找到了答案.基于此，我对 Eli Bendersky's example 做了一个小改动。 :

更新:此代码已在 Windows 上的 Python 3.4 64 位和 Linux 上的 Python 3.5 64 位上进行了测试。对于 Windows 上的 Python 3.5，请参阅 eryksun 的评论。

from contextlib import contextmanager
import ctypes
import io
import os
import sys
import tempfile

import ctypes.util
from ctypes import *
import platform

if platform.system() == "Linux":
    libc = ctypes.CDLL(None)
    c_stdout = ctypes.c_void_p.in_dll(libc, 'stdout')
if platform.system() == "Windows":
    class FILE(ctypes.Structure):
        _fields_ = [
            ("_ptr", c_char_p),
            ("_cnt", c_int),
            ("_base", c_char_p),
            ("_flag", c_int),
            ("_file", c_int),
            ("_charbuf", c_int),
            ("_bufsize", c_int),
            ("_tmpfname", c_char_p),
        ]

    # Gives you the name of the library that you should really use (and then load through ctypes.CDLL
    msvcrt = CDLL(ctypes.util.find_msvcrt())
    libc = msvcrt # libc was used in the original example in _redirect_stdout()
    iob_func = msvcrt.__iob_func
    iob_func.restype = POINTER(FILE)
    iob_func.argtypes = []

    array = iob_func()

    s_stdin = addressof(array[0])
    c_stdout = addressof(array[1])


@contextmanager
def stdout_redirector(stream):
    # The original fd stdout points to. Usually 1 on POSIX systems.
    original_stdout_fd = sys.stdout.fileno()

    def _redirect_stdout(to_fd):
        """Redirect stdout to the given file descriptor."""
        # Flush the C-level buffer stdout
        libc.fflush(c_stdout)
        # Flush and close sys.stdout - also closes the file descriptor (fd)
        sys.stdout.close()
        # Make original_stdout_fd point to the same file as to_fd
        os.dup2(to_fd, original_stdout_fd)
        # Create a new sys.stdout that points to the redirected fd
        sys.stdout = io.TextIOWrapper(os.fdopen(original_stdout_fd, 'wb'))

    # Save a copy of the original stdout fd in saved_stdout_fd
    saved_stdout_fd = os.dup(original_stdout_fd)
    try:
        # Create a temporary file and redirect stdout to it
        tfile = tempfile.TemporaryFile(mode='w+b')
        _redirect_stdout(tfile.fileno())
        # Yield to caller, then redirect stdout back to the saved fd
        yield
        _redirect_stdout(saved_stdout_fd)
        # Copy contents of temporary file to the given stream
        tfile.flush()
        tfile.seek(0, io.SEEK_SET)
        stream.write(tfile.read())
    finally:
        tfile.close()
        os.close(saved_stdout_fd)

if __name__ == '__main__':
    f = io.BytesIO()
    print('...')

    with stdout_redirector(f):
        print('foobar')
        print(12)
        libc.puts(b'this comes from C')
        os.system('echo and this is from echo')

    print('Got stdout:"\n{0}\n"'.format(f.getvalue().decode('utf-8')))

    print('Resuming normal operation...')