redirect_* should also redirect C-level streams

[masklinn]

BPO	44157
Nosy	@masklinn

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-05-17.12:32:33.510>
labels = ['type-feature', 'library', '3.9']
title = 'redirect_* should also redirect C-level streams'
updated_at = <Date 2021-05-17.12:32:33.510>
user = 'https://github.com/masklinn'

bugs.python.org fields:

activity = <Date 2021-05-17.12:32:33.510>
actor = 'xmorel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-05-17.12:32:33.510>
creator = 'xmorel'
dependencies = []
files = []
hgrepos = []
issue_num = 44157
keywords = []
message_count = 1.0
messages = ['393810']
nosy_count = 1.0
nosy_names = ['xmorel']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue44157'
versions = ['Python 3.9']

[masklinn]

In 3.4 (resp. 3.5), redirect_stdout and redirect_stderr were added to provide easy and reentrant stream redirection. Although that is documented, it seems like a waste that they only redirect the high-level sys.std* streams: those are already pretty easy to redirect by simply setting the corresponding attribute, which is essentially what the contextmanager does. However,

• that does not work if the writer has imported the original stream object (from sys import stderr)
• that does not work if the writer bypasses or is not aware of the Python layer e.g. a native library

In that case, the user still has to deal with dup/dup2 dances in order to redirect the underlying fds, which is significantly more error-prone (and verbose) than intercepting the high-level sys.std* ever was.

On the other hand, it's also less expressive as it requires an actual fd, rather than a Python-level file-like object. So I can understand not doing it by default.

But still, I think I feel like it'd be very useful to either expand the existing context managers to perform fd redirection, or have a separate context manager able to redirect arbitrary fds.