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。
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。
根据这个答案:https://stackoverflow.com/a/5916874/1060344，这是我在我的一个项目中使用的另一种方法。无论你用什么替换sys。Stderr或sys。stderr/ Stdout被用在一些不受你控制的库中，你必须确保替换符合文件接口，特别是当你这样做的时候。该库可能正在使用文件对象的其他方法。
以这种方式检查，我仍然让所有内容都执行stderr/stdout(或任何文件)，并使用Python的日志记录功能将消息发送到日志文件(但你真的可以用它做任何事情):
class FileToLogInterface(file):
'''
Interface to make sure that everytime anything is written to stderr, it is
also forwarded to a file.
'''
def __init__(self, *args, **kwargs):
if 'cfg' not in kwargs:
raise TypeError('argument cfg is required.')
else:
if not isinstance(kwargs['cfg'], config.Config):
raise TypeError(
'argument cfg should be a valid '
'PostSegmentation configuration object i.e. '
'postsegmentation.config.Config')
self._cfg = kwargs['cfg']
kwargs.pop('cfg')
self._logger = logging.getlogger('access_log')
super(FileToLogInterface, self).__init__(*args, **kwargs)
def write(self, msg):
super(FileToLogInterface, self).write(msg)
self._logger.info(msg)
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
