bpo-41147 Document that redirect_stdout provides the new stream as context var #21199

PeterJCLaw · 2020-06-28T12:43:07Z

In contextlib, _RedirectStream (the class behind redirect_stdout and redirect_stderr) returns the current stream target as its context variable, which allows code like this:

with redirect_stdout(io.StringIO()) as buffer:
    do_stuff()

use(buffer.getvalue())

where you capture the redirected stream without a separate line to declare the variable.

This PR intends to document this functionality.

https://bugs.python.org/issue41147

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Doc/library/contextlib.rst

"context variable" is not a clear term in light of the `contextvars` module.

PeterJCLaw · 2020-08-21T11:31:23Z

@JelleZijlstra would you have time to have another look at this?

JelleZijlstra

Looks good apart from this typo. I don't have the permissions to merge this PR though.

Doc/library/contextlib.rst

csabella · 2020-09-21T12:35:51Z

@PeterJCLaw, please sign the CLA. Thank you!

PeterJCLaw · 2020-09-21T20:14:33Z

@PeterJCLaw, please sign the CLA. Thank you!

Most odd. I signed it back in June when I opened this PR (I have a confirmation email to that effect), though the CLA now shows that I've not signed one. Anyway, I've signed another. The only difference I can see is that the first one I did used the email address I have on bugs.python.org; this time I've used the same email address as I commit with.

PeterJCLaw · 2020-10-10T13:16:56Z

@csabella is there anything I can do to help progress this?

iritkatriel · 2021-01-08T19:55:48Z

Doc/library/contextlib.rst

@@ -236,10 +236,11 @@ Functions and classes provided:

   For example, the output of :func:`help` normally is sent to *sys.stdout*.
   You can capture that output in a string by redirecting the output to an
-   :class:`io.StringIO` object::
+   :class:`io.StringIO` object. For convenience, the new stream is returned


It's not necessarily a new stream.

Hrm, I was meaning new in the sense of now being the one used for stdout. Perhaps "replacement" would be clearer?

Sorry I missed your reaction earlier in the year. I've now made this change (in 14d7692).

Doc/library/contextlib.rst

bedevere-bot · 2021-05-20T19:05:44Z

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

PeterJCLaw · 2021-05-23T12:54:33Z

@bedevere-bot I have made the requested changes; please review again.

bedevere-bot · 2021-05-23T12:54:36Z

Thanks for making the requested changes!

@iritkatriel: please review the changes made to this pull request.

iritkatriel · 2021-05-23T18:34:28Z

@rhettinger Are you happy for this to be a documented feature?

iritkatriel · 2021-05-26T13:49:02Z

This is actually covered by a unit test: test_enter_result_is_target

cpython/Lib/test/test_contextlib.py

Line 960 in 14d7692

def test_enter_result_is_target(self):

miss-islington · 2021-05-26T14:13:12Z

Thanks @PeterJCLaw for the PR, and @iritkatriel for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10, 3.9.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

… as context var (pythonGH-21199) (cherry picked from commit 46db39d) Co-authored-by: Peter Law <[email protected]>

bedevere-bot · 2021-05-26T14:13:27Z

GH-26379 is a backport of this pull request to the 3.10 branch.

… as context var (pythonGH-21199) (cherry picked from commit 46db39d) Co-authored-by: Peter Law <[email protected]>

bedevere-bot · 2021-05-26T14:13:31Z

GH-26380 is a backport of this pull request to the 3.9 branch.

… as context var (GH-21199) (GH-26379) (cherry picked from commit 46db39d) Co-authored-by: Peter Law <[email protected]>

… as context var (GH-21199) (GH-26380) (cherry picked from commit 46db39d) Co-authored-by: Peter Law <[email protected]>

Document that redirect_stdout provides the new stream as context var

cdcf0b7

See https://bugs.python.org/issue41147.

PeterJCLaw requested a review from 1st1 as a code owner June 28, 2020 12:43

the-knights-who-say-ni added the CLA not signed label Jun 28, 2020

bedevere-bot added docs Documentation in the Doc dir awaiting review labels Jun 28, 2020

PeterJCLaw commented Jun 28, 2020

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Be explicit that the new stream ends up in the context var

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PeterJCLaw commented Jul 3, 2020

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PeterJCLaw added 2 commits July 17, 2020 15:16

Clarify that we mean the target of the with statement

67c22ce

"context variable" is not a clear term in light of the `contextvars` module.

Properly quote this

a533a2e

JelleZijlstra approved these changes Aug 21, 2020

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Fix typo

40dcc50

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iritkatriel reviewed Jan 8, 2021

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The replacement stream is not neccesarily new

14d7692

bedevere-bot added awaiting change review and removed awaiting changes labels May 23, 2021

bedevere-bot requested a review from iritkatriel May 23, 2021 12:54

iritkatriel approved these changes May 26, 2021

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iritkatriel added needs backport to 3.9 only security fixes needs backport to 3.10 only security fixes labels May 26, 2021

iritkatriel approved these changes May 26, 2021

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iritkatriel merged commit 46db39d into python:main May 26, 2021

bedevere-bot removed the awaiting merge label May 26, 2021

bedevere-bot removed the needs backport to 3.10 only security fixes label May 26, 2021

bedevere-bot removed the needs backport to 3.9 only security fixes label May 26, 2021

iritkatriel pushed a commit that referenced this pull request May 26, 2021

bpo-41147: [doc] contextlib.redirect_stdout() provides the new stream…

1261941

… as context var (GH-21199) (GH-26379) (cherry picked from commit 46db39d) Co-authored-by: Peter Law <[email protected]>

iritkatriel pushed a commit that referenced this pull request May 26, 2021

bpo-41147: [doc] contextlib.redirect_stdout() provides the new stream…

bee66d3

… as context var (GH-21199) (GH-26380) (cherry picked from commit 46db39d) Co-authored-by: Peter Law <[email protected]>

pablogsal mentioned this pull request Jul 18, 2021

[3.10] Correct the order of regen-abidump #27228

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PeterJCLaw deleted the bpo-41147-document-redirect-stdout-uses-context-variable branch January 16, 2022 21:27

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bpo-41147 Document that redirect_stdout provides the new stream as context var #21199

bpo-41147 Document that redirect_stdout provides the new stream as context var #21199

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bpo-41147 Document that redirect_stdout provides the new stream as context var #21199

bpo-41147 Document that redirect_stdout provides the new stream as context var #21199

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