caching with comprehension list with if

Summary

Caching a function with a comprehension list with an if inside seem creates an error message.

Steps to reproduce

What are the steps we should take to reproduce the bug: Here’s a sample code:

import streamlit as st

@st.cache()
def create_raw_data():
    global production
    production=[[10 for m in range(3) if w>2] for w in range(5)]

create_raw_data()
st.write(production)

Expected behavior:

Actual behavior:

KeyError: 'w'
Streamlit encountered an error while caching the body of create_raw_data(). This is likely due to a bug in C:\Vincent\PycharmProjects\Streamlit_trials\Sugar\generator.py near line 6:
production=[[10 for m in range(3) if w>2] for w in range(5)]

Is this a regression?

I doesn’t seem so since I tried this with several versions of streamlit and still got the same error message.

Debug info

• Streamlit version: (get it with $ streamlit version): 0.64
• Python version: (get it with $ python --version) Python 3.7 and Python 3.8
• Using Conda? PipEnv? PyEnv? Pex? Tried with conda and pipenv
• OS version: windows 10
• Browser version: chrome 84.0

Additional information

It seems that the if statement is the culprit here, if removed the code is cached nicely.

[vhfgosselin]

Yes, this wasn’t solved. The go-around for me in my real code ( I just provided here a simple example) was to do what jrhone suggested:

replace: [[10 for m in range(3) if w>2] for w in range(5)] by [[10 for m in range(3)] for w in range(5) if w > 2]

although this is not exactly the same thing.

So in summary, there is a bug still it seems.

[randyzwitch]

Closing as a wontfix, given the new st.memo and st.singleton functionality Streamlit is moving toward. If this same issue persists in that new functionality, please let us know!