The whole category in one page.
SET UP EVERY PROJECT THE SAME WAY
Python 3, a virtual environment, pinned dependencies in a requirements file, configuration and secrets outside the code, and version control with the ignore file configured before the first commit.
THE THREE RULES THAT PREVENT MOST SECURITY PROBLEMS
Parameterise every database query, without exception. Escape everything displayed in a page. Validate every input at the server, regardless of browser checks.
And never leave debug mode enabled in production.
NEVER USE ORDINARY DECIMAL NUMBERS FOR MONEY
They cannot represent some values exactly. Use a decimal type designed for exact arithmetic.
ON YOUR HOSTING
cPanel's Python application feature creates the environment and serves the application.
It runs as a persistent process, so restart after any code, dependency or environment change. That is the most common report of all.
For cron, use full paths to both the interpreter and the script — cron inherits nothing.
WHEN SOMETHING FAILS
Read the traceback from the bottom, and the application log first.
Print the value and its type when a result surprises you.
BEFORE OPTIMISING, MEASURE
The assumption about where time goes is usually wrong, and the commonest cause is work repeated inside a loop.
THE TEST FOR ANYTHING YOU BUILD
Could a competent person set this up and change it safely, from the repository alone?
