Cannot build xeus-python-demo

[nthiery]

Description

xeus-python-demo won't build. I first encountered this on a jupyter lite instance of mine.
It presumably is related to the version of conda/mamba.

Reproduce

1. Install a fresh miniforge3
2. Install mamba
3. Create build environment with mamba env create -f build-environment.yml
4. Switch to build environment with mamba activate build-env
5. Run jupyter-lite build --contents content --output-dir dist

Got

RuntimeError: Failed to create the virtual environment for xeus-python,
        please make sure at least mamba, micromamba or conda is installed.

Full log

jupyter-lite build --contents content --output-dir dist
static:jupyter-lite.json
.  pre_status:static:jupyter-lite.json
    tarball:         jupyterlite-app-0.5.0.tgz 14MB
    output:          /opt/xeus-python-demo/dist
    lite dir:        /opt/xeus-python-demo
    apps:            
    sourcemaps:      True
    unused packages: True
archive:archive
contents:contents
icons:icons
lite:jupyter-lite.json
mimetypes:jupyter-lite.json
serve:contents
settings:overrides
translation:translation
.  status:archive:archive
[LiteBuildApp] No archive (yet): xeus-python-demo-jupyterlite.tgz
.  status:contents:contents
    contents: 2 files
.  status:icons:icons
    favicon files: 7 files
.  status:lite:jupyter-lite.json
[LiteBuildApp]     jupyter-lite.(json|ipynb): 0 files
.  status:mimetypes:jupyter-lite.json
    filetypes:         26 
.  status:serve:contents
    url: http://127.0.0.1:8000/
    server: tornado
    headers:
.  status:settings:overrides
    overrides.json: 0
.  status:translation:translation
    translation files: 2 files
static:output_dir
-- pre_init:static:output_dir
static:unpack
-- init:static:unpack
federated_extensions:copy:ext:jupyterlab_pygments
federated_extensions:copy:ext:@jupyterlite/xeus-extension
-- pre_build:federated_extensions:copy:ext:jupyterlab_pygments
-- pre_build:federated_extensions:copy:ext:@jupyterlite/xeus-extension
contents:copy:README.md
contents:copy:demo.ipynb
icons:copy
/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/jupyterlite_core/addons/translation.py:89: UserWarning: [lite] [translation] install `jupyterlab_server` to load translations: No module named 'jupyterlab_server'
  if not self.is_sys_prefix_ignored() and has_optional_dependency(
translation:copy
-- build:contents:copy:README.md
-- build:contents:copy:demo.ipynb
.  build:icons:copy
-- build:translation:copy
contents:contents:.
federated_extensions:patch
federated_extensions:settings
[LiteBuildApp] ERROR | [lite] [post_build] [jupyterlite-xeus] [ERR] Failed to create the virtual environment for xeus-python,
        please make sure at least mamba, micromamba or conda is installed.
Traceback (most recent call last):

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/doit_cmd.py", line 294, in run

return command.parse_execute(args)

~~~~~~~~~~~~~~~~~~~~~^^^^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/cmd_base.py", line 150, in parse_execute

return self.execute(params, args)

~~~~~~~~~~~~^^^^^^^^^^^^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/cmd_base.py", line 570, in execute

return self._execute(**exec_params)

~~~~~~~~~~~~~^^^^^^^^^^^^^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/cmd_run.py", line 265, in _execute

return runner.run_all(self.control.task_dispatcher())

~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/runner.py", line 254, in run_all

self.run_tasks(task_dispatcher)

~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/runner.py", line 213, in run_tasks

node = task_dispatcher.generator.send(node)

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/control.py", line 629, in _dispatcher_generator

next_step = node.step()

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/control.py", line 336, in step

return next(self.generator)

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/control.py", line 345, in _func

for value in decorated(*args, **kwargs):

~~~~~~~~~^^^^^^^^^^^^^^^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/control.py", line 473, in _add_task

new_tasks = generate_tasks(to_load, task_gen, ref.doc)

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/loader.py", line 390, in generate_tasks

for task_dict, x_doc in flat_generator(gen_result, gen_doc):

~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/doit/loader.py", line 27, in flat_generator

for item in gen:

^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/jupyterlite_core/manager.py", line 138, in _delayed_gather

yield from _gather()

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/jupyterlite_core/manager.py", line 131, in _gather

raise error

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/jupyterlite_core/manager.py", line 123, in _gather

for task in getattr(addon, attr)(self):

~~~~~~~~~~~~~~~~~~~~^^^^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/jupyterlite_xeus/add_on.py", line 138, in post_build

self.create_prefix()

~~~~~~~~~~~~~~~~~~^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/jupyterlite_xeus/add_on.py", line 162, in create_prefix

create_conda_env_from_env_file(root_prefix, yaml_content, env_file.parent)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/jupyterlite_xeus/create_conda_env.py", line 53, in create_conda_env_from_env_file

create_conda_env_from_specs(

~~~~~~~~~~~~~~~~~~~~~~~~~~~^

env_name=env_name,

^^^^^^^^^^^^^^^^^^

...<3 lines>...

pip_dependencies=pip_dependencies,

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

)

^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/jupyterlite_xeus/create_conda_env.py", line 69, in create_conda_env_from_specs

_create_conda_env_from_specs_impl(

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^

env_name=env_name,

^^^^^^^^^^^^^^^^^^

...<2 lines>...

channels=channels,

^^^^^^^^^^^^^^^^^^

)

^

File "/opt/miniforge3/envs/build-env/lib/python3.13/site-packages/jupyterlite_xeus/create_conda_env.py", line 131, in _create_conda_env_from_specs_impl

raise RuntimeError(

...<3 lines>...

)

RuntimeError: Failed to create the virtual environment for xeus-python,

please make sure at least mamba, micromamba or conda is installed.

Expected behavior

A smooth run

Context

• JupyterLite version:

(build-env) ➜  xeus-python-demo git:(main) ✗ mamba --version
2.0.5
(build-env) ➜  xeus-python-demo git:(main) ✗ conda --version
conda 25.1.0
(build-env) ➜  xeus-python-demo git:(main) ✗ mamba list | grep jupyterlite
  jupyterlite-core               0.5.0           pyh885dcc9_0        conda-forge
  jupyterlite-xeus               3.1.1           pyhd8ed1ab_0        conda-forge

• Operating System and version: Linux ubuntu 24.10
• Browser and version: firefox; but not used anyway

[martinRenou]

Thanks for opening an issue.

This is weird. Can you try installing micromamba from conda-forge into build-env?

[nthiery]

Ah ah, good catch. Thanks for the tip. That worked :-)

Should micromamba be added to build-environment.yml? Or should it work with just conda/mamba?

[martinRenou]

It is supposed to work with just conda/mamba, although we've seen some issues with them.

We're thinking of dropping support for them and simply depend on micromamba jupyterlite/xeus#148