factory_method

id	creational/factory_method
name	Factory Method
aliases	virtual-constructor class-attribute-factory
guide_url	https://python-patterns.guide/gang-of-four/factory-method/
problem	Let a class defer which helper object it constructs, so subclasses or callers can substitute another.
symptoms	subclass to change what gets built framework builds objects the app must customize response_class-style override
verdict	prefer-alternative
caveats	The guide's dodge is Dependency Injection: if you already have the object, pass the object, not a method that builds it. When creation must stay inside the class, prefer a class attribute factory (override by assignment or subclass) over an abstract method — any callable can be plugged in.
stdlib_sightings	http.client.HTTPConnection.response_class json.JSONDecoder

Factory Method

Let a class defer which helper it constructs, so subclasses, callers, or tests substitute another. Verdict: prefer an alternative — inject the object, or make the constructor call a class-attribute slot; the abstract-method form is Java with the serial numbers filed off.

Where	What
pattern/	The importable code: factory_slot (trap-safe class-attribute factories) and the Factory alias; the three dodges — injection, class-attribute slot, instance override — documented best first
docs/	Fundamentals · Implementation guide · External examples
examples/feed_client/	Mini-project: a feed-client framework with a response_class slot
tests/	Behavioral tests for the pattern and the mini-project

uv run python -m patterns.creational.factory_method.examples.feed_client.main