Sprint 9-10 - Modular Callback Structure for Multi-Tab Dashboards

Date: 2026-01-17 Tags: dash, callbacks, architecture, python, code-organization, maintainability

Context

Implementing a 5-tab Toronto Neighbourhood Dashboard with multiple callbacks per tab (map updates, chart updates, KPI updates, selection handling).

Problem

Initial callback implementation approach would have placed all callbacks in a single file, leading to:

A monolithic file with 500+ lines
Difficult-to-navigate code
Callbacks for different tabs interleaved
Testing difficulties

Solution

Organized callbacks into three focused modules:

callbacks/
├── __init__.py              # Imports all modules to register callbacks
├── map_callbacks.py         # Choropleth updates, map click handling
├── chart_callbacks.py       # Supporting chart updates (scatter, trend, donut)
└── selection_callbacks.py   # Dropdown population, KPI updates

Key patterns:

Group by responsibility, not by tab - all map-related callbacks together
Use noqa comments for imports that register callbacks as side effects
Share helper functions (like _empty_chart()) within modules

# callbacks/__init__.py
from . import (
    chart_callbacks,  # noqa: F401
    map_callbacks,  # noqa: F401
    selection_callbacks,  # noqa: F401
)

Prevention

Plan callback organization before implementation - sketch which callbacks go where
Group by function, not by feature - keeps related logic together
Keep modules under 400 lines - split if exceeding
Test imports early - verify callbacks register correctly