ImportError: cannot load module more than once per process in compiled version of my NiceGui App - but not when running interpreted

[Lexstok]

First Check

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Example Code

I don't know exactly where in my code something goes wrong, as the error only references the NiceGUI code lines and not my code....

Description

I have written an internal application that runs fine while running from the written code.
It does an SQL query to retrieve some information, processes it and sets it up to display in mermaid.

However, an error appears when I compiled it via pyinstaller to an .exe to deploy to some colleagues.

The app compiles correctly, and starts up and functions as foreseen: I can enter data, the sql query happens, the result is retrieved, and the analysis happens.
However, before it gets to displaying the result, the compiled app gives the following error:

...
Found 8 timeline dates
Found 8 timeline values
Type is not JSON serializable: decimal.Decimal
Traceback (most recent call last):
  File "nicegui\json\orjson_wrapper.py", line 54, in _orjson_converter
    import numpy as np  # pylint: disable=import-outside-toplevel
    ^^^^^^^^^^^^^^^^^^
  File "PyInstaller\loader\pyimod02_importers.py", line 450, in exec_module
  File "numpy\__init__.py", line 125, in <module>
  File "PyInstaller\loader\pyimod02_importers.py", line 450, in exec_module
  File "numpy\__config__.py", line 4, in <module>
  File "PyInstaller\loader\pyimod02_importers.py", line 450, in exec_module
  File "numpy\_core\__init__.py", line 22, in <module>
  File "PyInstaller\loader\pyimod02_importers.py", line 450, in exec_module
  File "numpy\_core\multiarray.py", line 11, in <module>
**ImportError: cannot load module more than once per process** 
 
The above exception was the direct cause of the following exception:
 
Traceback (most recent call last):
  File "nicegui\outbox.py", line 132, in loop
    await coro
  File "nicegui\outbox.py", line 145, in _emit
    await core.sio.emit(message_type, data, room=client_id)
  File "socketio\async_server.py", line 178, in emit
  File "socketio\async_manager.py", line 39, in emit
  File "socketio\packet.py", line 64, in encode
  File "nicegui\json\orjson_wrapper.py", line 40, in dumps
    return orjson.dumps(obj, option=opts, default=_orjson_converter).decode('utf-8')
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: Type is not JSON serializable: decimal.Decimal

I suspect it's the IMPORTERROR but I have no clue on wether this is a pyinstaller problem (ie me creating the problem) OR something inside the nicegui code that needs to be fixed, so I post it here before creating a possible bug report.

Anybody have any ideas on what the possible problem is ?

NiceGUI Version

3.7.1

Python Version

3.12.9

Browser

Other

Operating System

Windows

Additional Context

No response

[evnchn]

Hello @Lexstok

If you have a Decimal object somewhere and you intend to pass it to NiceGUI component, you would need to cast it back into either a float or a str

The frontend knows nothing about the Python Decimal object, so we didn't design the serializer to handle it 🤷

[Lexstok]

Hello, @evnchn - thank you for your answer!
I can understand that, but then why does it work correctly when run from the commandline and not work when compiled to an exe ? Let me explain my (perhaps faulty) reasoning:

The first error states:

File "nicegui\json\orjson_wrapper.py", line 54, in orjson_converter
import numpy as np # pylint: disable=import-outside-toplevel
^^^^^^^^^^^^^^^^^^
<snip>
ImportError: cannot load module more than once per process

And then continues with:

The above exception was the direct cause of the following exception
<snip>

which is the decimal object error.

Because it states The above exception was the direct cause : wouldn't that mean that the first error is the import of numpy in the orjson_wrapper? Which then generates the second error about the Decimal object?

That would point to an import error loading numpy multiple times, which borks when the program is frozen using pyinstaller ?

[phifuh]

import numpy as np # pylint: disable=import-outside-toplevel
Why are you loading it outside of the toplevel?

[falkoschindler]

@phifuh NiceGUI imports NumPy conditionally inside the _orjson_converter.

[evnchn]

@Lexstok I think #5759 accidentally fixes your issue by making Decimal outbox-serializable.

Perhaps we may want to investigate something similar without the msgpack

[Lexstok]

Thank you @evnchn for your answer - it's still not clear to me if the original problem is not the conditional import of the numpy library that failed ? My python knowledge is not good enough to correctly understand the issue, apologies.

[evnchn]

This comment was written by Claude Code on behalf of @evnchn.

@Lexstok You are right — the root cause is importlib.util.find_spec("numpy") failing in compiled (e.g. PyInstaller) environments.

I have pushed a fix that replaces find_spec with a simple try/except import. Could you test it by installing from my branch?

pip install git+https://github.com/evnchn/nicegui.git@fix/numpy-import-compiled-exe

Please let me know if this resolves the issue for you. If it works, I will open a PR.

[Lexstok]

I will try tomorrow to install this, it's at work, so need to check if this is allowed by them.