René Cano
All projects

No. 12

Sales & inventory

Streamlit point of sale and inventory

My role
Sole author
Period
Nov 2025
Code

The problem

A small business needs to record sales, know what's in stock and hand out a receipt without paying for a point-of-sale system. I wanted to solve it with a simple web app on top of a real database.

What I built

I built it alone, in 10 commits from November 2 to 23, 2025.

  • A Streamlit app with 7 modules: dashboard, sales, products, purchases, expenses, reports and settings.
  • Sign-in with bcrypt passwords, a signed session cookie with expiry and 2 roles, admin and cashier. A kiosk mode hides purchases, expenses, reports and settings from anyone who isn't an admin.
  • Sales with a cart, configurable VAT and a PDF receipt generated with ReportLab.
  • Purchases that update stock and cost (last cost or weighted average), expense tracking, period reports with charts, CSV export and a ZIP backup of 7 tables.
  • PostgreSQL access through SQLAlchemy, with automatic commit or rollback per transaction.

Architecture

Architecture diagram: the admin or the cashier signs in with bcrypt and a signed cookie; the Streamlit app shows 7 modules depending on the role; the app reads and writes products, sales, purchases and expenses in PostgreSQL, generates PDF receipts with ReportLab, and exports CSV reports and a ZIP backup.

Results

There are no usage metrics to report. What can be checked is the code: the sale, purchase and reporting flows, and role-based access.

Known limits

  • Everything lives in a single 2,363-line app.py. Splitting data, domain and UI is the first thing I'd do.
  • The database schema was created by hand and isn't in the repository (init_db does nothing), so it can't be set up from scratch without rebuilding it.
  • There are no tests.
  • The README presents sign-in as optional or in progress, even though it's implemented.

Links