Python plugin fails on core26: base snap does not include Python interpreter
Metadata
Current evaluation
core26 lacks a Python runtime, so Python-plugin builds fail unless Python is staged. Documentation covers the workaround, and maintainers are pursuing clearer warning guidance.
Suggested action: keep open
Reason: @bepri confirmed the core26 requirement is documented and identified clearer warning guidance as the remaining work; @jahn-junior agreed and proposed linking the Python dependency documentation. BasePythonPlugin still falls back to a system interpreter and otherwise exits late with a generic message, leaving a valid but bounded diagnostics improvement open.
Evaluated by: mr-cal-bot
Impact:
45
Quick Win:
25
Complexity:
30
Confidence:
92
Actionability:
80
Issue body
### Bug Description
## Summary
The python plugin fails to build snaps targeting `core26` because the base snap no longer includes a Python interpreter. The plugin assumes Python will be available either in the staged payload or in the base, but core26 has removed Python from the base.
## Steps to Reproduce
1. Create a snap using the python plugin with `base: core26`
2. Run `snapcraft`
## Expected Behavior
Either:
- The python plugin automatically stages Python when the base doesn't include it, OR
- The plugin fails early with a clear error message instructing the user to add `python3-venv` to `stage-packages`
## Actual Behavior
The build fails late in the process with:
Looking for a Python interpreter called "python3.14" in the payload...
Python interpreter not found in payload.
No suitable Python interpreter found, giving up.
## Details
The `BasePythonPlugin` in `craft_parts/plugins/base.py`:
1. Declares `python3-dev` and `python3-venv` as **build-packages**
2. Creates a venv using the build environment's Python
3. Searches for Python in the payload (install_dir/stage_dir)
4. Falls back to `$(readlink -f "$(which python3)")` assuming it exists at runtime
This fallback worked when bases (core22, core24) included Python, but breaks on core26 where Python was removed.
$ ls /snap/core24/current/usr/bin/python*
/snap/core24/current/usr/bin/python3 -> python3.12
/snap/core24/current/usr/bin/python3.12
$ ls /snap/core26/current/usr/bin/python*
zsh: no matches found: /snap/core26/current/usr/bin/python*
## Ideas for a fix
**Auto-stage Python when needed**
- Detect when the target base lacks Python and automatically add `python3-venv` to stage-packages
**Fail early with guidance**
- Check for Python in the base during validation and emit a clear error:
```
Error: base 'core26' does not include Python. Add 'python3-venv' to stage-packages.
```
## Workaround
Manually add `python3-venv` to `stage-packages` in `snapcraft.yaml`.
## Environment
- snapcraft 9.0.1
- craft-parts (bundled with snapcraft)
- base: core26 (Ubuntu 26.04 / Resolute)
### part yaml
```shell
parts:
test:
plugin: python
source: .
build-packages:
- git
stage-packages:
- git
- openssh-client
python-packages:
- ./[...]
override-pull: |
craftctl default
craftctl set version="$(git describe --tags --always)"
```
### Relevant log output
```shell
:: 2026-08-10 18:24:49.949 :: + python3 -m venv /root/parts/[...]/install
:: 2026-08-10 18:24:49.949 :: Error: [Errno 13] Permission denied: '/root/parts/[...]/install/bin/python3'
:: 2026-08-10 18:24:49.949 Check the build output and verify the project can work with the 'python' plugin.
```
Evaluation history
| Date | Model | Scores | Action | Summary |
|---|---|---|---|---|
| stealth/space-bunny-alpha |
Impact:
45
Quick Win:
25
Complexity:
30
Confidence:
92
Actionability:
80
|
keep open | core26 lacks a Python runtime, so Python-plugin builds fail unless Python is staged. Documentation covers the workaround, and maintainers are pursuing clearer warning guidance. | |
| stealth/space-bunny-alpha |
Impact:
42
Quick Win:
25
Complexity:
32
Confidence:
93
Actionability:
88
|
keep open | Python plugin needs clearer guidance on core26, where the base lacks a Python interpreter; documented workaround is staging Python, and maintainers support adding a warning. | |
| qwen3.6-35b-a3b-mtp-q6 |
Impact:
50
Quick Win:
30
Staleness:
25
Complexity:
40
Confidence:
75
Support Request:
20
|
keep open | Python plugin fails on core26 base due to missing Python interpreter; maintainers suggest implementing clearer error guidance | |
| qwen/qwen3.6-35b-a3b |
Staleness:
5
Complexity:
15
Confidence:
90
Support Request:
10
|
needs triage | Python plugin fails on core26 due to missing Python interpreter in base. Maintainers are discussing adding a clearer error message to guide users to stage python3-venv. Currently under discussion. | |
| qwen/qwen3.6-35b-a3b |
Staleness:
5
Complexity:
40
Confidence:
90
Support Request:
20
|
needs triage | Python plugin fails building for core26 base due to missing Python interpreter. Currently unlabelled, awaiting maintainer triage and decision on whether to auto-stage Python or improve error messaging. | |
| qwen/qwen3.6-35b-a3b |
Staleness:
5
Complexity:
45
Confidence:
90
Support Request:
10
|
needs triage | Python plugin fails when targeting core26 base due to missing Python interpreter. Well-structured bug report with reproduction steps and proposed fixes, awaiting maintainer triage. |
Update history
| Date | Change |
|---|---|
| updated | |
| updated | |
| updated | |
| created |
Related work
-
Related To:
snapcraft#6020
(confidence 96%)
Tracks broader core26 Python-plugin build failures and records a Snapcraft-side fix for the standard plugin; it does not demonstrate that generic Craft Parts guidance was implemented.
Related issues
| Issue | Project | State | Summary | Similarity |
|---|---|---|---|---|
| #6020 Most Python-based snaps can't build on core26 | snapcraft | closed | Fixed by merged PR #6089 (commit 6ee41173c) and released in Snapcraft 8.14.3, enabling Python plugin builds on core26. | |
| #2161192 python plugin not working at all with snapcraft 9+ | snapcraft (launchpad) | open | Core26 Python plugin builds and module loading were fixed; packaging Python separately is now documented as required by the base. | |
| #786 Python plugin. Python is broken in core24 classic snaps if snap is used on an older Ubuntu LTS version | craft-parts | open | Core24 classic snaps using the Python plugin fail on older Ubuntu LTS hosts because staged Python cannot find its stdlib; Snapcraft 8.3.2's fix proved incomplete, with follow-up in snapcraft#5144. | |
| #1874920 python plugin doesn't support base "core20" | snapcraft (launchpad) | closed | Closed without a recorded fix after years of inactivity. Snapcraft 4.0 added core20 support, but i386 had no core20 base and external-symlink lint failures remained. | |
| #6089 fix(plugins/python): fix core26 builds | snapcraft | merged | Merged #6089 fixed #6020 by enabling the Python plugin for strictly confined core26 snaps and adding spread tests; released in Snapcraft 8.14.3. | |
| #1641 uv plugin fails on core26: dispatch script uses system Python instead of venv | craft-parts | open | core26 has no Python in the base snap, so uv-built parts find no interpreter in the payload and fall back to the system python, leaving venv/bin/python pointing at a bare interpreter that lacks ops. Fix options undecided. | |
| #5144 error out if core24 classic python snap is created with the non-staged python binary | snapcraft | open | Add a Python-plugin guard for classic snaps staged without the python3-minimal symlink; current post_prime only rewrites pyvenv.cfg, leaving the core24 failure mode unresolved. |