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Merged
merged 23 commits into from
Jul 21, 2025
Merged

gh-136251: Improvements to WASM demo REPL #136252

merged 23 commits into from
Jul 21, 2025

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adqm
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@adqm adqm commented Jul 3, 2025 •
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I'm including a couple of fixes for the WASM demo, which for me made the demo "just work" out of the box for me with a build from following the instructions on this page:

  • Exported HEAPU32 at build time since python.worker.mjs expects it to be there (for determining the version number)
  • Updated the HTML to properly load xterm.js

I also made a few changes to try to improve the usability of the web REPL, also included here:

  • Reset things when starting a new process (without this change, running the same program multiple times would not work, requiring a refresh)
  • Added support for arrow key navigation (and home/end) in the REPL (including history scrollback)
  • Added support for TAB and CTRL+C, trying to mimic the behavior of the regular of those inputs from the Python REPL
  • Replaced the textarea with Ace code editor.
  • Moved the demo to index.html instead of python.html so that the URL shown in the terminal when running server.py takes you to the demo (without needing to append /python.html)

I also put up a demo here that shows the result of a fresh Emscripten build with these changes.

There's definitely still room for improvement here (for example, #124621 suggests updating the demo to use PyREPL), but I'm sharing these changes in case they're useful in the meantime.

Related Issue: #136251

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@adqm adqm requested a review from brettcannon as a code owner July 3, 2025 17:52
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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

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sobolevn
sobolevn reviewed Jul 3, 2025
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not a full review, just saw some style problems :)

@brettcannon brettcannon removed their request for review July 3, 2025 21:01
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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

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adqm commented Jul 3, 2025

thanks, @sobolevn! i just ran prettier on that file; it looks like it caught those style issues and quite a few more.

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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

merwok
merwok reviewed Jul 5, 2025
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adqm commented Jul 16, 2025

Sorry for the delay here, @hoodmane ! I just pushed a few changes. I think I'm pretty happy with where things are right now, but definitely open to more feedback / suggestions / bug reports!

@merwok, if you're interested to take another look, I also updated the copy of the demo on my server: https://hz.mit.edu/wasm_repl_demo/

Here's what changed:

  • I was able to much more closely match the behavior of the regular Python REPL by using code.interact. The implementation there is a little hacky, but I think it works (with the exception that if someone gives a magic string as input, it gets treated as a ctrl+c press).
  • Input history is now stickier, by way of sessionStorage (if available). History should persist within a browsing session (including persisting across reloads) but should be cleared when closing the tab.
  • I added an error message when SharedArrayBuffer is not available. I'm certainly open to changing the words and/or the CSS, but here's what it looks like now if SharedArrayBuffer is undefined:
    wasm_repl_error_msg

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I broke this on the main branch again (in one place I check for process incorrectly and cause a crash). In order to avoid breaking it we'll need to add an in-browser smoke test to the emscripten buildbot.

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Merged main and pushed a commit fixing the problem. I'll run the Emscripten buildbot on this and if it passes it is good to merge.

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!buildbot emscripten

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🤖 New build scheduled with the buildbot fleet by @hoodmane for commit 26ddd07 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F136252%2Fmerge

The command will test the builders whose names match following regular expression: emscripten

The builders matched are:

  • WASM Emscripten PR

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Okay it needs the fix from #136909 to unbreak the buildbot...

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!buildbot emscripten

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🤖 New build scheduled with the buildbot fleet by @hoodmane for commit 7d33525 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F136252%2Fmerge

The command will test the builders whose names match following regular expression: emscripten

The builders matched are:

  • WASM Emscripten PR

@ambv ambv merged commit d1d526a into python:main Jul 21, 2025
41 checks passed
@hoodmane hoodmane added OS-emscripten topic-repl Related to the interactive shell needs backport to 3.14 bugs and security fixes labels Jul 21, 2025
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Thanks @adqm for the PR, and @ambv for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

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Sorry, @adqm and @ambv, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker d1d526afe7ce62c787b150652a2ba136cb949d74 3.14

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Looks like first we have to backport #136822.

@ambv ambv added needs backport to 3.14 bugs and security fixes and removed needs backport to 3.14 bugs and security fixes labels Jul 22, 2025
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Thanks @adqm for the PR, and @ambv for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Jul 22, 2025
@adqm @hoodmane @miss-islington
pythongh-136251: Improvements to WASM demo REPL (pythonGH-136252)
cf7b7fe 
(cherry picked from commit d1d526a)

Co-authored-by: adam j hartz <adam@smatz.net>
Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>
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bedevere-app bot commented Jul 22, 2025

GH-136977 is a backport of this pull request to the 3.14 branch.

@bedevere-app bedevere-app bot removed the needs backport to 3.14 bugs and security fixes label Jul 22, 2025
ambv pushed a commit that referenced this pull request Jul 22, 2025
@miss-islington @adqm @hoodmane
[3.14] gh-136251: Improvements to WASM demo REPL (GH-136252) (GH-136977)
4f1f648 
(cherry picked from commit d1d526a)

Co-authored-by: adam j hartz <adam@smatz.net>
Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>
taegyunkim pushed a commit to taegyunkim/cpython that referenced this pull request Aug 4, 2025
@adqm @hoodmane @taegyunkim
pythongh-136251: Improvements to WASM demo REPL (pythonGH-136252)
265158f 
Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>
Agent-Hellboy pushed a commit to Agent-Hellboy/cpython that referenced this pull request Aug 19, 2025
@adqm @hoodmane @Agent-Hellboy
pythongh-136251: Improvements to WASM demo REPL (pythonGH-136252)
d38c4bb 
Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>
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