如何在Python中将标准输出重定向到任意文件?
When a long-running Python script (e.g, web application) is started from within the ssh session and backgounded, and the ssh session is closed, the application will raise IOError and fail the moment it tries to write to stdout. I needed to find a way to make the application and modules output to a file rather than stdout to prevent failure due to IOError. Currently, I employ nohup to redirect output to a file, and that gets the job done, but I was wondering if there was a way to do it without using nohup, out of curiosity.
我已经试过了。Stdout = open('somefile'， 'w')，但这似乎并没有阻止一些外部模块仍然输出到终端(或者sys. exe)。Stdout =…Line根本没有开火)。我知道它应该在我测试过的更简单的脚本上工作，但我还没有时间在web应用程序上进行测试。
基于这篇文章之前的回答，我为自己编写了这个类，作为一种更紧凑和灵活的方式来重定向代码段的输出——这里只是一个列表——并确保之后的输出是规范化的。
class out_to_lt():
def __init__(self, lt):
if type(lt) == list:
self.lt = lt
else:
raise Exception("Need to pass a list")
def __enter__(self):
import sys
self._sys = sys
self._stdout = sys.stdout
sys.stdout = self
return self
def write(self,txt):
self.lt.append(txt)
def __exit__(self, type, value, traceback):
self._sys.stdout = self._stdout
用作:
lt = []
with out_to_lt(lt) as o:
print("Test 123\n\n")
print(help(str))
更新。刚刚发现了一个场景，我必须添加两个额外的方法，但很容易适应:
class out_to_lt():
...
def isatty(self):
return True #True: You're running in a real terminal, False:You're being piped, redirected, cron
def flush(self):
pass
您需要一个终端多路复用器，比如tmux或GNU屏幕
我很惊讶Ryan Amos对原始问题的一个小评论是唯一一个比其他所有问题都更可取的解决方案，不管蟒蛇的诡计有多聪明，他们得到了多少点赞。根据Ryan的评论，tmux是GNU屏幕的一个很好的替代品。
But the principle is the same: if you ever find yourself wanting to leave a terminal job running while you log-out, head to the cafe for a sandwich, pop to the bathroom, go home (etc) and then later, reconnect to your terminal session from anywhere or any computer as though you'd never been away, terminal multiplexers are the answer. Think of them as VNC or remote desktop for terminal sessions. Anything else is a workaround. As a bonus, when the boss and/or partner comes in and you inadvertently ctrl-w / cmd-w your terminal window instead of your browser window with its dodgy content, you won't have lost the last 18 hours-worth of processing!
引用自PEP 343 -“with”语句(添加了import语句):
临时重定向标准输出:
import sys
from contextlib import contextmanager
@contextmanager
def stdout_redirected(new_stdout):
save_stdout = sys.stdout
sys.stdout = new_stdout
try:
yield None
finally:
sys.stdout = save_stdout
用途如下:
with open(filename, "w") as f:
with stdout_redirected(f):
print "Hello world"
当然，这不是线程安全的，但手动执行相同的操作也不是。在单线程程序(例如脚本)中，这是一种流行的做事方式。
基于这篇文章之前的回答，我为自己编写了这个类，作为一种更紧凑和灵活的方式来重定向代码段的输出——这里只是一个列表——并确保之后的输出是规范化的。
class out_to_lt():
def __init__(self, lt):
if type(lt) == list:
self.lt = lt
else:
raise Exception("Need to pass a list")
def __enter__(self):
import sys
self._sys = sys
self._stdout = sys.stdout
sys.stdout = self
return self
def write(self,txt):
self.lt.append(txt)
def __exit__(self, type, value, traceback):
self._sys.stdout = self._stdout
用作:
lt = []
with out_to_lt(lt) as o:
print("Test 123\n\n")
print(help(str))
更新。刚刚发现了一个场景，我必须添加两个额外的方法，但很容易适应:
class out_to_lt():
...
def isatty(self):
return True #True: You're running in a real terminal, False:You're being piped, redirected, cron
def flush(self):
pass
以下是Yuda Prawira的回答:
实现flush()和所有文件属性
将其编写为上下文管理器
也捕获stderr
.
import contextlib, sys
@contextlib.contextmanager
def log_print(file):
# capture all outputs to a log file while still printing it
class Logger:
def __init__(self, file):
self.terminal = sys.stdout
self.log = file
def write(self, message):
self.terminal.write(message)
self.log.write(message)
def __getattr__(self, attr):
return getattr(self.terminal, attr)
logger = Logger(file)
_stdout = sys.stdout
_stderr = sys.stderr
sys.stdout = logger
sys.stderr = logger
try:
yield logger.log
finally:
sys.stdout = _stdout
sys.stderr = _stderr
with log_print(open('mylogfile.log', 'w')):
print('hello world')
print('hello world on stderr', file=sys.stderr)
# you can capture the output to a string with:
# with log_print(io.StringIO()) as log:
# ....
# print('[captured output]', log.getvalue())
