Python 3.4中有contextlib.redirect_stdout()功能：
from contextlib import redirect_stdout
with open('help.txt', 'w') as f:
with redirect_stdout(f):
print('it now prints to `help.text`')
它类似于：
import sys
from contextlib import contextmanager
@contextmanager
def redirect_stdout(new_target):
old_target, sys.stdout = sys.stdout, new_target # replace sys.stdout
try:
yield new_target # run some code with the replaced stdout
finally:
sys.stdout = old_target # restore to the previous value
可以在早期的Python版本中使用。后一版本不可重用。如果需要，可以将其制成一个。
它不会在文件描述符级别重定向标准输出，例如：
import os
from contextlib import redirect_stdout
stdout_fd = sys.stdout.fileno()
with open('output.txt', 'w') as f, redirect_stdout(f):
print('redirected to a file')
os.write(stdout_fd, b'not redirected')
os.system('echo this also is not redirected')
b'not redirected'并且'echo this also is not redirected'不会重定向到该output.txt文件。
要在文件描述符级别重定向，os.dup2()可以使用：
import os
import sys
from contextlib import contextmanager
def fileno(file_or_fd):
fd = getattr(file_or_fd, 'fileno', lambda: file_or_fd)()
if not isinstance(fd, int):
raise ValueError("Expected a file (`.fileno()`) or a file descriptor")
return fd
@contextmanager
def stdout_redirected(to=os.devnull, stdout=None):
if stdout is None:
stdout = sys.stdout
stdout_fd = fileno(stdout)
# copy stdout_fd before it is overwritten
#NOTE: `copied` is inheritable on Windows when duplicating a standard stream
with os.fdopen(os.dup(stdout_fd), 'wb') as copied:
stdout.flush() # flush library buffers that dup2 knows nothing about
try:
os.dup2(fileno(to), stdout_fd) # $ exec >&to
except ValueError: # filename
with open(to, 'wb') as to_file:
os.dup2(to_file.fileno(), stdout_fd) # $ exec > to
try:
yield stdout # allow code to be run with the redirected stdout
finally:
# restore stdout to its previous value
#NOTE: dup2 makes stdout_fd inheritable unconditionally
stdout.flush()
os.dup2(copied.fileno(), stdout_fd) # $ exec >&copied
如果stdout_redirected()使用代替，则现在可以使用相同的示例redirect_stdout()：
import os
import sys
stdout_fd = sys.stdout.fileno()
with open('output.txt', 'w') as f, stdout_redirected(f):
print('redirected to a file')
os.write(stdout_fd, b'it is redirected now\n')
os.system('echo this is also redirected')
print('this is goes back to stdout')
output.txt只要stdout_redirected()上下文管理器处于活动状态，以前打印在stdout上的输出现在将保留。
注意：stdout.flush()不会在直接在其上实现I / O的Python 3上刷新C stdio缓冲区read() / write()系统调用。要刷新所有打开的C stdio输出流，libc.fflush(None)如果某些C扩展使用基于stdio的I / O ，则可以显式调用：
try:
import ctypes
from ctypes.util import find_library
except ImportError:
libc = None
else:
try:
libc = ctypes.cdll.msvcrt # Windows
except OSError:
libc = ctypes.cdll.LoadLibrary(find_library('c'))
def flush(stream):
try:
libc.fflush(None)
stream.flush()
except (AttributeError, ValueError, IOError):
pass # unsupported
您可以使用stdout参数来重定向其他流，而不仅仅是sys.stdout合并sys.stderr和sys.stdout：
def merged_stderr_stdout(): # $ exec 2>&1
return stdout_redirected(to=sys.stdout, stdout=sys.stderr)
例：
from __future__ import print_function
import sys
with merged_stderr_stdout():
print('this is printed on stdout')
print('this is also printed on stdout', file=sys.stderr)
注意：stdout_redirected()混合使用缓冲的I / O（sys.stdout通常）和未缓冲的I / O（直接对文件描述符进行操作）。当心，可能会有缓冲 问题。
要回答，请进行编辑：您可以python-daemon用来守护脚本并使用logging模块（如@ erikb85建议）代替print语句，而仅将stdout重定向到您nohup现在运行的长期运行的Python脚本。
script.p > file