[Python-ideas] Replacing the standard IO streams (was Re: changing sys.stdout encoding) (original) (raw)

Paul Moore p.f.moore at gmail.com
Sat Jun 9 13:00:37 CEST 2012

On 9 June 2012 10:55, Nick Coghlan <ncoghlan at gmail.com> wrote:

So, after much digging, it appears the right way to replace a standard stream in Python 3 after application start is to do the following:

 sys.stdin = open(sys.stdin.fileno(), 'r', )  sys.stdout = open(sys.stdout.fileno(), 'w', )  sys.stderr = open(sys.stderr.fileno(), 'w', ) Ditto for the other standard streams. It seems it already is as simple as with any other file, we just collectively forgot about:

One minor point - if sys.stdout is redirected, and you have already written to sys.stdout, this resets the file pointer. With test.py as

import sys print("Hello!") sys.stdout = open(sys.stdout.fileno(), 'w', encoding='utf-8') print("Hello!")

test.py >a gives one line in a, not two (tested on Windows, Unix may be different). And changing to "a" doesn't resolve this...

Of course, the actual use case is to change the encoding before anything is written - so maybe a small note saying "don't do this" is enough. But it's worth mentioning before we get the bug report saying "Python lost my data" :-)

Paul.

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