python的subprocess为什么要有close_fd参数?

cdsfiui

例如，建立一个子进程，如果调用者打开了fd=0,1,2(标准输入，输出，错误)和fd=3(文件 ./a.txt)，那么用subprocess.POpen建立一个子进程的时候，如果设置了"close_fd=True"，比如:

1.     p=subprocess.Popen(cmd,shell=True,close_fds=True,stdout=None...

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那么这是否意味着在子进程中:

(1) fd 0-3都已经被关闭了?
(2) 如果都关闭了，那么调用者如何通过管道和子进程做输入、输出的交互呢?

1. p.communicate()

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看起来就不能工作了，对吗?

但是我看到不少代码都有上面两句，先close_fds=True,然后communicate()

所以疑惑了，还请解释一下

MMMIX

回复 1# cdsfiui

https://docs.python.org/3/library/subprocess.html

If close_fds is true, all file descriptors except 0, 1 and 2 will be closed before the child process is executed. (POSIX only). The default varies by platform: Always true on POSIX. On Windows it is true when stdin/stdout/stderr are None, false otherwise. On Windows, if close_fds is true then no handles will be inherited by the child process. Note that on Windows, you cannot set close_fds to true and also redirect the standard handles by setting stdin, stdout or stderr.