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Backend Developer Guide

Technology Stack​

  • FastAPI — Async Python web framework
  • Uvicorn — ASGI server
  • SQLAlchemy (async) — ORM for PostgreSQL
  • psycopg2 — Sync PostgreSQL driver (used in background tasks)
  • pandas — Data processing for NSE bhav copies
  • Pydantic v2 — Request/response validation

Project Structure​

backend/
├── app/
│   ├── api/                # FastAPI route modules
│   │   ├── bhav_downloader.py
│   │   ├── stocks.py
│   │   ├── fo.py
│   │   └── ...
│   ├── database/
│   │   └── session.py      # Async DB session factory
│   ├── config.py           # Config class (APP_ENV, CSV_PATH, AMI_PATH, ...)
│   └── main.py             # App factory, router registration
├── nseeod/                 # NSE data ingestion package
│   ├── downloadbhav.py     # BhavProcessor orchestrator
│   ├── EquityBhav.py       # Equity segment updater
│   ├── FoBhav.py           # F&O segment updater
│   ├── bhav.py             # AMI format generator
│   ├── pgs.py              # psycopg2 connection helpers
│   └── utils.py            # NSE working days, holiday calendar
├── requirements.txt
└── .env

Key Modules​

app/config.py​

Reads environment variables to build paths:

class Config:
    APP_ENV = os.getenv("APP_ENV", "LOCAL")
    CSV_PATH = os.getenv("LOCAL_CSV_PATH") if APP_ENV == "LOCAL" else os.getenv("VPS_CSV_PATH")
    AMI_PATH = os.getenv("LOCAL_AMI_PATH") if APP_ENV == "LOCAL" else os.getenv("VPS_AMI_PATH")

nseeod/downloadbhav.py — BhavProcessor​

Orchestrates the full bhav download pipeline:

MethodDescription
run_update()Full catch-up sync for all missing dates
run_update_for_date(date)Force-sync a single specific date
_generate_ami(date)Generate AmiBroker export (never raises)
AddLog(msg, source)Append to stats.json log list
AddHistory(date, status, msg)Append to history list

Background Task Flow​

POST /api/bhav-downloader/download
  └── BackgroundTasks.add_task(processor.run_update)
         └── Runs after HTTP response is sent
                └── Writes progress to stats.json
                       └── Frontend polls GET /api/bhav-downloader/status

Running the Backend​

cd backend
uvicorn app.main:app --reload --host 0.0.0.0 --port 8000

Adding a New API Route​

  1. Create backend/app/api/mymodule.py with an APIRouter.
  2. Register in app/main.py: 
    from app.api.mymodule import router as mymodule_router
    app.include_router(mymodule_router)

Running the NSE Module Standalone​

Always run from the backend/ directory using module syntax:

cd backend
python -m nseeod.downloadbhav

Do not use python nseeod\downloadbhav.py — this adds the wrong folder to sys.path.