Streamlit Best Practices Advanced

Build fast, maintainable, and secure Streamlit applications. This lesson covers performance optimization, app architecture patterns, security considerations, and tips for production-ready apps.

Performance Optimization

• Cache aggressively: Use @st.cache_data for all data loading and computation, @st.cache_resource for models and connections
• Use forms for batch input: Prevent unnecessary re-runs by grouping related inputs in st.form
• Lazy loading: Load data and models only when needed, not at the top of every script run
• Limit DataFrame size: Display subsets of large DataFrames; use pagination or filters
• Use st.fragment: For partial re-runs of specific sections without re-running the whole script
• Optimize images: Resize images before displaying; use st.image(width=...) to control render size

App Architecture

my-app/
  app.py                  # Main entry point
  pages/
    1_Dashboard.py        # Page 1
    2_Analysis.py         # Page 2
    3_Settings.py         # Page 3
  utils/
    data.py               # Data loading functions
    models.py             # ML model functions
    helpers.py            # Utility functions
  .streamlit/
    config.toml           # Streamlit configuration
    secrets.toml          # Local secrets (gitignored)
  requirements.txt
  .gitignore

Configuration

[theme]
primaryColor = "#FF4B4B"
backgroundColor = "#FFFFFF"
secondaryBackgroundColor = "#F0F2F6"
textColor = "#262730"
font = "sans serif"

[server]
maxUploadSize = 200
enableCORS = false
enableXsrfProtection = true

[browser]
gatherUsageStats = false

Security Best Practices

Common Patterns

Error Handling

try:
    result = process_data(user_input)
    st.success("Processing complete!")
    st.write(result)
except ValueError as e:
    st.error(f"Invalid input: {e}")
except Exception as e:
    st.error("An unexpected error occurred. Please try again.")
    st.exception(e)  # Show full traceback in dev mode

Loading States

if st.button("Process Data"):
    with st.spinner("Processing..."):
        result = long_running_function()
    st.success("Done!")
    st.balloons()  # Celebrate!

Testing

• Unit test utilities: Test your data processing and ML functions independently from Streamlit
• AppTest: Use streamlit.testing.v1.AppTest for automated UI testing
• Manual testing: Test across browsers and screen sizes
• Performance profiling: Use st.cache_data.clear() to test cold start performance

Production Checklist

• All sensitive values stored in secrets, not in code
• Error handling on all user inputs and API calls
• Loading indicators for slow operations
• Responsive layout tested on mobile
• Requirements pinned to specific versions
• st.set_page_config() called at the very top
• Cache decorators on all data loading and model functions
• Favicon and page title configured
• .gitignore includes .streamlit/secrets.toml