Dynamic Property Valuation Model with Machine Learning Integration

Create a Google Sheets add-on using Python and Apps Script that dynamically calculates property valuations by integrating machine learning predictive models. The solution should pull real-time market data, apply regression algorithms from scikit-learn, and automatically update a live dashboard with confidence intervals, predicted appreciation rates, and comparative market analysis. Implement error handling for data inconsistencies and provide visualizations that can be refreshed with a single button click.