Trade a 2^N subclass table for N wrappers that share one interface, stack compression and encryption around a file source in any order, and spot the same nesting in new BufferedReader(new FileReader(f)) and Python's open().

A FileDataSource with read and write ships fine, until someone wants compressed saves, then encrypted ones, then both. By the third option you're naming a CompressedEncryptedFileDataSource and the class names are multiplying faster than the features.

Collapse a recursive if isinstance(node, Folder) into one size() that both files and folders answer, watch the type check leave the caller and become recursion on the container, and weigh the transparency-versus-safety cost of putting add() on every node.

Your total_size(node) function opens with if isinstance(node, Folder), recurses into the children, and re-asks the same question at every level. Add a zip-archive node and you're back editing that one function, and every other function that walks the tree.

Wrap a vendor's dispatch(to, body, opts) so two hundred call sites keep calling send(msg), watch the translation live entirely inside the wrapper, and tell it from a decorator by the one thing that differs: the interface changes, not the behaviour.

Your whole app calls notify.send(msg). The SMS vendor you just signed names the same action dispatch, wants a recipient and an options bag, and there are two hundred call sites between you and a library you can't edit.

Front an expensive or guarded object with a same-interface stand-in that decides when to create it, whether to allow the call, or whether a cached answer is enough, and spot the shape in JS new Proxy, ORM lazy loads, and gRPC stubs.

A photo grid builds a full-resolution HighResImage for all two hundred files the moment the folder opens, decoding megabytes the user scrolls past. The screen shows nine at a time; the rest loaded for nothing.

Route a handler's five service calls through one method so callers depend on one class instead of five, reach past it straight to a worker for the rare case the method skips, and split the front before it bloats into a god object.

A checkout handler calls inventory.reserve, then payment.charge, then shipping.schedule, then emails the buyer, in that exact order. Every screen that places an order copies the same five-step dance and imports all five classes.