gh-141395: Clarify stdout flush behavior for newline characters in print()#142094
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Vemulakonda559 wants to merge 10 commits intopython:mainfrom
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gh-141395: Clarify stdout flush behavior for newline characters in print()#142094Vemulakonda559 wants to merge 10 commits intopython:mainfrom
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Hello! I’ve updated the branch to be up to date with |
This PR adds a note to the print() documentation to clarify how Python’s stdout buffering works with newline (\n) characters inside a single print call. Motivation: Current documentation mentions that flush() is implied for writes containing newlines. However, it does not explain that Python flushes only after the entire write operation, not mid-string. This can confuse users coming from C, who expect a flush at each newline, and developers writing scripts that rely on immediate output for progress indicators or CLI feedback. What’s added: A .. note:: block explaining that stdout behavior depends on the environment (TTY vs redirected stdout). Guidance on explicitly flushing with flush=True or sys.stdout.flush(). Mention of python -u for unbuffered output. A short example demonstrating the behavior. Impact: Improves clarity for learners and developers. Aligns documentation with actual behavior across different environments. Not a behavior change — documentation-only PR. Related Issue: Addresses issue python#141395
Removed duplicate text and improved clarity in the note about stdout flushing behavior.
Removed redundant sentence about output buffering.
Removed unnecessary comments about string flushing in print.
Remove extra blank lines and fix indentation for versionchanged directive.
Reformat output buffering explanation for clarity.
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Hi, kindly requesting a review when time permits. I’m happy to update the PR based on any feedback. |
nedbat
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Jan 17, 2026
| Output buffering is usually determined by *file*. However, if *flush* is | ||
| true, the stream is forcibly flushed. | ||
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| .. note:: |
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In my opinion, this note is unnecessary. Python never intended to behave as C does. We've already said that flush forcibly flushes.
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I agree with Ned. |
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This PR adds a note to the print() documentation to clarify how Python’s stdout buffering works with newline (\n) characters inside a single print call.
Motivation:
Current documentation mentions that flush() is implied for writes containing newlines.
However, it does not explain that Python flushes only after the entire write operation, not mid-string.
This can confuse users coming from C, who expect a flush at each newline, and developers writing scripts that rely on immediate output for progress indicators or CLI feedback.
What’s added:
A .. note:: block explaining that stdout behavior depends on the environment (TTY vs redirected stdout).
Guidance on explicitly flushing with flush=True or sys.stdout.flush().
Mention of python -u for unbuffered output.
A short example demonstrating the behavior.
Impact:
Improves clarity for learners and developers.
Aligns documentation with actual behavior across different environments.
Not a behavior change — documentation-only PR.
Related Issue:
Addresses issue #141395
📚 Documentation preview 📚: https://cpython-previews--142094.org.readthedocs.build/