Skip to content

Instantly share code, notes, and snippets.

@natedileas

natedileas/redirect.py

Last active Aug 24, 2020
Embed
What would you like to do?
c-level stdout redirection on windows
""" Tested on Windows 10, 64 bit, Python 3.6
Sources:
https://eli.thegreenplace.net/2015/redirecting-all-kinds-of-stdout-in-python/
https://stackoverflow.com/questions/17942874/stdout-redirection-with-ctypes
"""
from contextlib import contextmanager
import ctypes
import io
import os, sys
import tempfile
### ALL THIS IS NEW ########################################
if sys.version_info < (3, 5):
libc = ctypes.CDLL(ctypes.util.find_library('c'))
else:
if hasattr(sys, 'gettotalrefcount'): # debug build
libc = ctypes.CDLL('ucrtbased')
else:
libc = ctypes.CDLL('api-ms-win-crt-stdio-l1-1-0')
# c_stdout = ctypes.c_void_p.in_dll(libc, 'stdout')
kernel32 = ctypes.WinDLL('kernel32')
STD_OUTPUT_HANDLE = -11
c_stdout = kernel32.GetStdHandle(STD_OUTPUT_HANDLE)
##############################################################
@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(None) #### CHANGED THIS ARG TO NONE #############
# 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)
#### Test it
f = io.BytesIO()
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: "{0}"'.format(f.getvalue().decode('utf-8')))
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.