Strategy

Swap interchangeable algorithms at runtime

Strategy captures a family of algorithms behind one interface so you can pick which to use at runtime. Pricing has several strategies — flat, surge, member-discount — and the right one depends on the booking. The calculator doesn't care which; it just applies the strategy it's given.

Say it plainly: in Python a strategy is almost always just a callable — a function or lambda you pass in. No Strategy base class, no subclass per algorithm.