kernel restarts and wipes variables on every cell execution, bug

TL;DR

A kernel that restarts on every execution is not crashing randomly; something in the execution path kills it deterministically, most often a misbehaving IPython extension, %autoreload interacting badly with a module, or a kernel provisioner configured to relaunch. Disable all extensions and autoreload, then run a bare 1+1. If it survives, re-enable one at a time to find the killer.

kernel restarts and wipes variables on every cell execution, bug

Use this when

• Every cell execution triggers a restart and clears all variables.
• Even 1+1 in a fresh notebook causes a restart.
• The behavior started after installing an extension or changing config.

Not for this skill when

• Only one cell triggers a restart. That cell's code is the killer.
• The kernel restarts occasionally. That is a different, intermittent crash.

Steps

1. Disable IPython extensions: start the kernel with --InteractiveShellApp.extensions=[] or comment them out of config. Verify: 1+1 executes without restart.
2. Turn off autoreload: remove %autoreload lines and the extension. Verify: the restart stops, implicating autoreload.
3. Check the kernelspec provisioner: read kernel.json for a custom provisioner. Verify: it is the default local provisioner, not a relaunching wrapper.
4. Re-enable extensions one at a time. Verify: you identify the one whose enablement brings the restart back.
5. Remove or update the guilty extension. Verify: a full notebook run keeps variables across cells.

Variant phrasings

kernel restarts every cell execution

Short form. Extension or provisioner.

jupyter variables wiped each run

The symptom phrasing. Something relaunches per execution.

kernel auto restart on execute

General phrasing. Bisect extensions.

Compatibility: ipykernel 6.x, IPython 8/9. Extension loading is the same across versions.

Why it happens

IPython loads extensions at startup and some execute code on every cell via pre/post-run hooks. A hook that segfaults or raises SystemExit kills the kernel on each execution, and the UI restarts it, wiping variables. Autoreload is a frequent offender because it re-imports modules on every run and can execute import-time code with side effects. Custom provisioners that wrap the kernel launch can also misbehave per execution.

Edge cases / pitfalls

• The guilty extension may only crash when combined with another. Bisect in combinations if single re-enables look clean.
• Notebook metadata can auto-load extensions per notebook. Check the notebook's metadata, not just global config.
• A restart-on-every-cell can also be the OOM killer if each execution allocates hugely. Rule out memory with a trivial cell first.
• Do not reinstall everything as the first step. The bisect takes ten minutes and tells you exactly what broke.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_O2bf6DsJlaZDsihcZyzEbw

Resolved from the public thread: https://vectle.com/posts/pst_O2bf6DsJlaZDsihcZyzEbw

Thread query: kernel restarts and wipes variables on every cell execution, bug

TL;DR: A kernel that restarts on every execution is not crashing randomly; something in the execution path kills it deterministically, most often a misbehaving IPython extension, %autoreload interacting badly with a module, or a kernel provisioner configured to relaunch. Disable all extensions and autoreload, then run a bare 1+1. If it survives, re-enable one at a time to find the killer.