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Add redirect_stdout(..., per_thread: bool = False)#167

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Liam-DeVoe wants to merge 3 commits intoQuansight-Labs:mainfrom
Liam-DeVoe:redirect-stdout
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Add redirect_stdout(..., per_thread: bool = False)#167
Liam-DeVoe wants to merge 3 commits intoQuansight-Labs:mainfrom
Liam-DeVoe:redirect-stdout

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@Liam-DeVoe
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@Liam-DeVoe Liam-DeVoe commented Jan 19, 2026

Closes #29.

This design takes inspiration from the design sketched by @colesbury in python/cpython#130148 (comment), with some changes required to support interleaving per_thread=False and per_thread=True.

If a per_thread=False context manager is entered (from any thread) while a per_thread=True context manager is active in some thread A, output from A will go to the per_thread=False stream. IMO this matches the expectation that redirect_stdout captures all output from all threads; if you don't want this behavior, pass per_thread=True.

This test illustrates the new thread–isolation capabilities:

n_threads = 10
barrier1 = Barrier(n_threads)
barrier2 = Barrier(n_threads)
bufs = [StringIO() for _ in range(n_threads)]

def f(n, stream):
    barrier1.wait()
    with redirect_stdout(stream, per_thread=True):
        print(f"thread {n}")
        barrier2.wait()

threads = [Thread(target=f, args=(i, bufs[i])) for i in range(n_threads)]

for t in threads:
    t.start()
for t in threads:
    t.join()

for i in range(n_threads):
    assert bufs[i].getvalue() == f"thread {i}\n"

Liam-DeVoe
Liam-DeVoe commented Jan 19, 2026
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Comment thread .gitignore
Comment on lines +1 to +2
.claude/settings.local.json

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@Liam-DeVoe Liam-DeVoe Jan 19, 2026

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(I used claude to iterate on this design, but I stand by every line in this PR myself!)

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@ferdnyc ferdnyc Jan 25, 2026

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That's cool, but please don't add personal files to project .gitignores. That's what .git/info/exclude is for.

  • Patterns which are specific to a particular repository but which do not need to be shared with other related repositories (e.g., auxiliary files that live inside the repository but are specific to one user’s workflow) should go into the $GIT_DIR/info/exclude file.

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@ferdnyc ferdnyc Jan 25, 2026

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(To be clear, when I say "that's cool", it's a completely meaningless phrase because I'm not a committer here, and I have no idea what the project policy is on AI contributions. It may be cool, or it may be very not cool.) ¯\_(ツ)_/¯

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@Liam-DeVoe Liam-DeVoe Jan 25, 2026 •
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While I agree in principle, in practice, if one expects a tool to be used by multiple developers, it's pragmatic to add that tool's ignorable files to the project's .gitignore.

For example, projects generally gitignore editor config files like .vscode/, even though the project is not related to any specific editor.

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@rgommers rgommers Jan 25, 2026

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Agreed, this is perfectly fine to add

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Liam-DeVoe commented Jan 19, 2026 •
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@Liam-DeVoe Liam-DeVoe mentioned this pull request Jan 19, 2026
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lysnikolaou
lysnikolaou reviewed Jan 20, 2026
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Really amazing work @Liam-DeVoe! Great set of tests as well!

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ngoldbaum commented Jan 20, 2026

@Liam-DeVoe I'm planning to go over this with you a little bit during our meeting later today.

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Liam-DeVoe commented Jan 20, 2026

Yup sounds like a great use of time 👍

@Liam-DeVoe Liam-DeVoe mentioned this pull request Jan 30, 2026
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Provide a facility for thread-safe stdout/stderr redirection

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@Liam-DeVoe @ngoldbaum @rgommers @ferdnyc @lysnikolaou