临时重定向 stdout/stderr [英] Temporarily Redirect stdout/stderr

问题描述

是否可以在 Python 中临时重定向 stdout/stderr(即在方法的持续时间内)?

Is it possible to temporarily redirect stdout/stderr in Python (i.e. for the duration of a method)?

当前解决方案的问题(我起初记得但后来忘记了)是它们不重定向；相反，它们只是完全替换了流.因此，如果一个方法有一个本地副本，因为任何原因(例如，因为流作为参数传递给某物)，它就不会工作.

The problem with the current solutions (which I at first remembered but then forgot) is that they don't redirect; rather, they just replace the streams in their entirety. Hence, if a method has a local copy of one the variable for any reason (e.g. because the stream was passed as a parameter to something), it won't work.

有什么解决办法吗?

推荐答案

解决某些函数可能将 sys.stdout 流缓存为局部变量从而替换全局 的问题sys.stdout 在该函数内不起作用，您可以在文件描述符级别重定向 (sys.stdout.fileno()) 例如:

To solve the issue that some function might have cached sys.stdout stream as a local variable and therefore replacing the global sys.stdout won't work inside that function, you could redirect at a file descriptor level (sys.stdout.fileno()) e.g.:

from __future__ import print_function
import os
import sys

def some_function_with_cached_sys_stdout(stdout=sys.stdout):
    print('cached stdout', file=stdout)

with stdout_redirected(to=os.devnull), merged_stderr_stdout():
    print('stdout goes to devnull')
    some_function_with_cached_sys_stdout()
    print('stderr also goes to stdout that goes to devnull', file=sys.stderr)
print('stdout is back')
some_function_with_cached_sys_stdout()
print('stderr is back', file=sys.stderr)

stdout_redirected() 重定向 sys.stdout.fileno() 到给定的文件名、文件对象或文件描述符(示例中为 os.devnull).

stdout_redirected() redirects all output for sys.stdout.fileno() to a given filename, file object, or file descriptor (os.devnull in the example).

stdout_redirected() 和 merged_stderr_stdout() 在这里定义.

stdout_redirected() and merged_stderr_stdout() are defined here.

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