import third party library in worker script #2403

chenkianwee · 2025-11-10T23:05:50Z

chenkianwee
Nov 10, 2025

Hi I am trying to use the web worker to run some computation heavy task at the background. I activate the worker.py in my main.py

worker = PyWorker("./worker.py", type="pyodide")
print("before ready")
await worker.ready
print("after ready")

In my worker.py file

from pyscript import sync
import numpy as np

def heavy_compute():
    res = np.array(1,2,3) # some computation that requires numpy
    return res

sync.heavy_compute = heavy_compute

However whenever i run my code I get the no module name numpy error. Why is that the case? I can import numpy in my main.py file and perform the computation there.

before ready
254c0ff1-da19-4885-9852-8f09221538b9:1 PythonError: Traceback (most recent call last):
  File "/lib/python313.zip/_pyodide/_base.py", line 523, in eval_code
    .run(globals, locals)
     ~~~^^^^^^^^^^^^^^^^^
  File "/lib/python313.zip/_pyodide/_base.py", line 357, in run
    coroutine = eval(self.code, globals, locals)
  File "<exec>", line 4, in <module>
ModuleNotFoundError: No module named 'numpy'
The module 'numpy-tests' is included in the Pyodide distribution, but it is not installed.
You can install it by calling:
  await micropip.install("numpy-tests") in Python, or
  await pyodide.loadPackage("numpy-tests") in JavaScript
See https://pyodide.org/en/stable/usage/loading-packages.html for more details.

    at new_error (pyodide.asm.js:8:578922)
    at pyodide.asm.wasm:0x10f082
    at pyodide.asm.wasm:0x10f14a
    at callPyObjectKwargs (pyodide.asm.js:8:632930)
    at Proxy.callKwargs (pyodide.asm.js:8:651089)
    at Object.runPython (pyodide.asm.js:8:683102)
    at Object.Pn (254c0ff1-da19-4885-9852-8f09221538b9:1:21241)
    at Object.run (254c0ff1-da19-4885-9852-8f09221538b9:1:33833)
    at Object.run (254c0ff1-da19-4885-9852-8f09221538b9:1:55819)
    at 254c0ff1-da19-4885-9852-8f09221538b9:1:56876
Pn @ 254c0ff1-da19-4885-9852-8f09221538b9:1
(anonymous) @ 254c0ff1-da19-4885-9852-8f09221538b9:1
(anonymous) @ 254c0ff1-da19-4885-9852-8f09221538b9:1
(anonymous) @ 254c0ff1-da19-4885-9852-8f09221538b9:1
await in (anonymous)
(anonymous) @ 254c0ff1-da19-4885-9852-8f09221538b9:1
pyodide.asm.js:8 after ready

thanks

WebReflection · 2025-11-11T08:30:31Z

WebReflection
Nov 11, 2025
Maintainer

you need to pass a config that contains all packages you want to list but also, if that's all you need to do (heavy Python computations to pass along the main thread) I suggest you testing the pyscript bridge: https://github.com/pyscript/pyscript/tree/main/bridge#readme

0 replies

chenkianwee · 2025-11-11T14:13:06Z

chenkianwee
Nov 11, 2025
Author

I tried passing the config file using this html tag but it is still not working. How do I pass the config file to the worker?

<script type="py" src="./worker.py" config="./pyscript.toml" worker></script>

Thanks I will take a look at pyscript bridge and see how I can use it in my case.

3 replies

chenkianwee Nov 11, 2025
Author

I have been trying to pass config to the worker with the following code.

worker = PyWorker("./worker.py", type="pyodide", config = "./worker_config.json")
print("before ready")
await worker.ready
print("after ready")

worker_config.json

{
    "packages": ["numpy"]
}

It seems like the passing of config is successful but I get this following error

fbbeecd0-7daf-438a-a290-fcefee7929f3:1 Loading micropip
fbbeecd0-7daf-438a-a290-fcefee7929f3:1 Loaded micropip
fbbeecd0-7daf-438a-a290-fcefee7929f3:1 Loading numpy
fbbeecd0-7daf-438a-a290-fcefee7929f3:1 Loaded numpy
fbbeecd0-7daf-438a-a290-fcefee7929f3:1 PythonError: Traceback (most recent call last):
  File "/lib/python313.zip/_pyodide/_base.py", line 523, in eval_code
    .run(globals, locals)
     ~~~^^^^^^^^^^^^^^^^^
  File "/lib/python313.zip/_pyodide/_base.py", line 357, in run
    coroutine = eval(self.code, globals, locals)
  File "<exec>", line 35, in <module>
  File "/home/pyodide/pyscript/__init__.py", line 2, in <module>
    from pyscript.magic_js import RUNNING_IN_WORKER,PyWorker,config,current_target,document,js_import,js_modules,sync,window
  File "/home/pyodide/pyscript/magic_js.py", line 7, in <module>
    else:config['type']='py'
         ~~~~~~^^^^^^^^
TypeError: 'str' object does not support item assignment

    at new_error (pyodide.asm.js:8:578922)
    at pyodide.asm.wasm:0x10f082
    at pyodide.asm.wasm:0x10f14a
    at callPyObjectKwargs (pyodide.asm.js:8:632930)
    at Proxy.callKwargs (pyodide.asm.js:8:651089)
    at Object.runPython (pyodide.asm.js:8:683102)
    at Object.Pn (fbbeecd0-7daf-438a-a290-fcefee7929f3:1:21241)
    at Object.run (fbbeecd0-7daf-438a-a290-fcefee7929f3:1:33833)
    at Object.run (fbbeecd0-7daf-438a-a290-fcefee7929f3:1:55799)
    at fbbeecd0-7daf-438a-a290-fcefee7929f3:1:56876
Pn @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
(anonymous) @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
(anonymous) @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
(anonymous) @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
await in (anonymous)
(anonymous) @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
fbbeecd0-7daf-438a-a290-fcefee7929f3:1 PythonError: Traceback (most recent call last):
  File "/lib/python313.zip/_pyodide/_base.py", line 523, in eval_code
    .run(globals, locals)
     ~~~^^^^^^^^^^^^^^^^^
  File "/lib/python313.zip/_pyodide/_base.py", line 357, in run
    coroutine = eval(self.code, globals, locals)
  File "<exec>", line 2, in <module>
  File "/home/pyodide/pyscript/__init__.py", line 2, in <module>
    from pyscript.magic_js import RUNNING_IN_WORKER,PyWorker,config,current_target,document,js_import,js_modules,sync,window
  File "/home/pyodide/pyscript/magic_js.py", line 7, in <module>
    else:config['type']='py'
         ~~~~~~^^^^^^^^
TypeError: 'str' object does not support item assignment

    at new_error (pyodide.asm.js:8:578922)
    at pyodide.asm.wasm:0x10f082
    at pyodide.asm.wasm:0x10f14a
    at callPyObjectKwargs (pyodide.asm.js:8:632930)
    at Proxy.callKwargs (pyodide.asm.js:8:651089)
    at Object.runPython (pyodide.asm.js:8:683102)
    at Object.Pn (fbbeecd0-7daf-438a-a290-fcefee7929f3:1:21241)
    at Object.run (fbbeecd0-7daf-438a-a290-fcefee7929f3:1:33833)
    at Object.run (fbbeecd0-7daf-438a-a290-fcefee7929f3:1:55819)
    at fbbeecd0-7daf-438a-a290-fcefee7929f3:1:56876
Pn @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
(anonymous) @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
(anonymous) @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
(anonymous) @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
await in (anonymous)
(anonymous) @ fbbeecd0-7daf-438a-a290-fcefee7929f3:1
pyodide.asm.js:8 after ready
pyodide.asm.js:8 TypeError: Cannot read properties of undefined (reading 'apply')

WebReflection Nov 12, 2025
Maintainer

can you try with this instead?

worker = PyWorker("./worker.py", type="pyodide", config={ "packages": ["numpy"] })

chenkianwee Nov 12, 2025
Author

Thanks !! Its working now !!

WebReflection · 2025-11-13T08:26:50Z

WebReflection
Nov 13, 2025
Maintainer

as this discussion's topic is solved, I've filed an issue to track the PyWorker config pre-resolution in here: #2404

Closing this as it's been solved and it was not an issue, just lack of details while bootstrapping the PyWorker.

0 replies

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