RuntimeError: There is no current event loop in thread error with Streamlit and Asyncio #744
Description
Summary
I am running pyppeteer, which depends on asyncio, to load data which is only available in a rendered web page. I experienced an error earlier with Jupyter, which depends on tornado, and where I received an error that RuntimeError: This event loop is already running. The reason is that tornado was reworked with asyncio and there didn't seem to be a realistic workaround by the Jupyter developers. The issue was solved with this library nest_asyncio. Whether I include nest_asyncio or not, I receive the error RuntimeError: There is no current event loop in thread 'ScriptRunner.scriptThread'.
Steps to reproduce
What are the steps we should take to reproduce the bug:
- Initializing the RenderHTML class in the following imported file, will cause the error to be outputted as an error to the Streamlit UI.
import asyncio
import nest_asyncio
#nest_asyncio.apply()
from pyppeteer import launch
class HTMLMissing(Exception):
'''An exception for a missing or invalid HTML.'''
pass
class RenderHTML():
def __init__(self, html=None):
self.html = ""
self.set_html(html)
asyncio.get_event_loop().run_until_complete(self.build_page())
async def build_page(self):
browser = await launch()
context = await browser.createIncognitoBrowserContext()
self.page = await browser.newPage()
...other functions...
Expected behavior:
Load RenderHTML class, launch chrome, and build a new browser page.
Actual behavior:
With: nest_asyncio.apply()
RuntimeError: There is no current event loop in thread 'ScriptRunner.scriptThread'.
Traceback:
File "c:\users\jroak\anaconda3\envs\project\lib\site-packages\streamlit\ScriptRunner.py", line 311, in _run_script
exec(code, module.__dict__)
File "D:\AnacondaProjects\DataProject\main.py", line 25, in <module>
from engine import *
File "D:\AnacondaProjects\DataProject\engine.py", line 25, in <module>
from lib import *
File "D:\AnacondaProjects\DataProject\lib\__init__.py", line 34, in <module>
from .renderer import RenderHTML
File "D:\AnacondaProjects\DataProject\lib\renderer.py", line 55, in <module>
nest_asyncio.apply()
File "c:\users\jroak\anaconda3\envs\project\lib\site-packages\nest_asyncio.py", line 11, in apply
loop = loop or asyncio.get_event_loop()
File "c:\users\jroak\anaconda3\envs\project\lib\asyncio\events.py", line 644, in get_event_loop
% threading.current_thread().name)
Without: nest_asyncio.apply()
RuntimeError: There is no current event loop in thread 'ScriptRunner.scriptThread'.
Traceback:
File "c:\users\jroak\anaconda3\envs\project\lib\site-packages\streamlit\ScriptRunner.py", line 311, in _run_script
exec(code, module.__dict__)
File "D:\AnacondaProjects\DataProject\main.py", line 94, in <module>
main()
File "D:\AnacondaProjects\DataProject\main.py", line 71, in main
crawler = render_data(crawler)
File "c:\users\jroak\anaconda3\envs\project\lib\site-packages\streamlit\caching.py", line 560, in wrapped_func
return get_or_set_cache()
File "c:\users\jroak\anaconda3\envs\project\lib\site-packages\streamlit\caching.py", line 540, in get_or_set_cache
return_value = func(*args, **kwargs)
File "D:\AnacondaProjects\DataProject\main.py", line 39, in render_data
crawler.render()
File "D:\AnacondaProjects\DataProject\engine.py", line 126, in render
renderer = RenderHTML()
File "D:\AnacondaProjects\DataProject\lib\renderer.py", line 72, in __init__
asyncio.get_event_loop().run_until_complete(self.build_page())
File "c:\users\jroak\anaconda3\envs\project\lib\asyncio\events.py", line 644, in get_event_loop
% threading.current_thread().name)
Is this a regression?
That is, did this use to work the way you expected in the past? IDK
yes / no
Debug info
- Streamlit version: 0.50.2
- Python version: 3.7.5
- Using Conda? PipEnv? PyEnv? Pex? Conda
- OS version: Windows 10
- Browser version: 70.0.1 (64-bit)
Additional information
If needed, add any other context about the problem here. For exmaple, did this bug come from https://discuss.streamlit.io or another site? Link the original source here!