Convert process can still encounter decoding errors

[MaxLohove]

Describe the bug

The issue at hand is similar to #540.
It concerns the conversion of jupyter notebook files in utf-8 format to marimo notebooks.

marimo convert my_notebook.ipynb > my_app.py

marimo convert my_notebook.ipynb -o my_app.py
Traceback (most recent call last):
File "", line 198, in _run_module_as_main
File "", line 88, in run_code
File "<my_path>.venv\Scripts\marimo.exe_main.py", line 8, in
sys.exit(main())
~~~~^^
File "<my_path>.venv\Lib\site-packages\click\core.py", line 1157, in call
return self.main(*args, **kwargs)
~~~~~~~~~^^^^^^^^^^^^^^^^^
File "<my_path>.venv\Lib\site-packages\click\core.py", line 1078, in main
rv = self.invoke(ctx)
File "<my_path>.venv\Lib\site-packages\click\core.py", line 1688, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
File "<my_path>.venv\Lib\site-packages\click\core.py", line 1434, in invoke
return ctx.invoke(self.callback, **ctx.params)
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "<my_path>.venv\Lib\site-packages\click\core.py", line 783, in invoke
return __callback(*args, **kwargs)
File "<my_path>.venv\Lib\site-packages\marimo_cli\convert\commands.py", line 68, in convert
f.write(notebook)
~~~~~~~^^^^^^^^^^
File "C:\Users\mlohove\AppData\Roaming\uv\python\cpython-3.13.0-windows-x86_64-none\Lib\encodings\cp1252.py", line 19, in encode
return codecs.charmap_encode(input,self.errors,encoding_table)[0]
~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
UnicodeEncodeError: 'charmap' codec can't encode characters in position 395-397: character maps to

I was able to trace the error to

if output:
        # Make dirs if needed
        maybe_make_dirs(output)
        with open(output, "w") as f:
            f.write(notebook)
        echo(f"Converted notebook saved to {output}")
    else:
        echo(notebook)

in marimo/_cli/convert/commands.py

Replacing
with open(output, "w") as f:
with
open(output, "w", encoding="utf-8") as f:

Allowed me to convert my notebook.

marimo convert my_notebook.ipynb -o my_app.py
Converted notebook saved to my_app.py

Environment

{
"marimo": "0.9.28",
"OS": "Windows",
"OS Version": "11",
"Processor": "Intel64 Family 6 Model 142 Stepping 10, GenuineIntel",
"Python Version": "3.13.0",
"Binaries": {
"Browser": "131.0.6778.86",
"Node": "v18.16.0"
},
"Dependencies": {
"click": "8.1.7",
"docutils": "0.21.2",
"itsdangerous": "2.2.0",
"jedi": "0.19.1",
"markdown": "3.7",
"narwhals": "1.15.1",
"packaging": "24.1",
"psutil": "6.0.0",
"pygments": "2.18.0",
"pymdown-extensions": "10.12",
"pyyaml": "6.0.2",
"ruff": "0.8.1",
"starlette": "0.41.3",
"tomlkit": "0.13.2",
"typing-extensions": "4.12.2",
"uvicorn": "0.32.1",
"websockets": "14.1"
},
"Optional Dependencies": {
"pandas": "2.2.3",
"pyarrow": "18.1.0"
}
}

Code to reproduce

No response

[mscolnick]

thanks for the issue and fix! i will put up a PR for your suggested fix.

is it odd the tests pass on windows (ill look into this)