Question about project-structure

[Eric]

my projects consist of severeal folders, with a main.py file running the programm and calling different functions in those folders.

In one usecase the main.py performs a database query and passes a pandas dataframe to sentiment.py. Inside the sentiment.py streamlit is beeing called to present the data.

Now each time i filter the data in streamlit, the main.py runs again, causing another database-query.

What would be the best or easiest way to prevent this from happening?

[dataprofessor]

Hi @Eric,

Perhaps you could structure your app as a multipage app. This could be done by creating a directory called pages and moving cleanup.py, sentiment.py and sql.py into it. As for various utility functions you can house it within a utility.py and import them.

I’ve created a simple example of a multipage app that you can try out:

• GitHub repo of the example multipage app GitHub - dataprofessor/st-multipage
• Try out the Demo app https://dataprofessor-st-multipage-home-1eb79e.streamlitapp.com/

Below is an example of the directory structure of the example multipage app.

├─ .streamlit
│  └─ config.toml
├─ pages
│  ├─ 1_🍎_Apples.py
│  ├─ 2_🍊_Oranges.py
│  └─ 3_🍐_Pear.py
├─ tools
│  └─ utility.py
├─ Home.py
├─ README.md
├─ packages.txt
├─ requirements.txt
└─ utilities.py

Resources to check out about Multipage apps:

• Multipage apps - Streamlit Docs
• Create a multipage app - Streamlit Docs
• Introducing multipage apps! 📄

[Eric]

Sorry, but i don’t understand how this structure is going to prevent rerunning my functionalities.

[dataprofessor]

Sorry, I forgot to also mention that you should also look into st.session_state which allows variables to be shared between pages that in turn allows carrying per-session state across multiple pages.

Every app interaction (e.g. changing values of input widgets) would cause the app to re-run. To prevent that you’ll have to use session state in your app.

Below are additional resources that you can look into which provides ample examples as well:

• Session State basics - YouTube
• Store Information Across App Interactions | Session State
• Session State - Streamlit Docs
• Add statefulness to apps - Streamlit Docs

[blackary]

I think the most important thing you need to do is simply use st.experimental_memo to cache the results of your database query. st.experimental_memo - Streamlit Docs

I don’t see any obvious issues with your structure, but this is the classic reason to use st.experimental_memo – your script is going to re-run lots of times as you interact with the app, and you don’t want to rerun everything, so you put things like database queries inside of a function decorated with @st.experimental_memo

[Eric]

@blackary

@st.experimental_memo

Thats what i was lokking for! I ttried the cache decorated before, thinking it would do the same, but never got it wokring. This works perfectly. Thanks!