What is the __init_subclass__ for plugin registration?

Question

Accepted Answer

**__init_subclass__** auto-registers subclasses in a **plugin system**.

```python
class Plugin:
    _registry = {}

def __init_subclass__(cls, name=None, **kwargs):
        super().__init_subclass__(**kwargs)
        plugin_name = name or cls.__name__.lower()
        Plugin._registry[plugin_name] = cls

@classmethod
    def get_plugin(cls, name):
        return cls._registry.get(name)

@classmethod
    def list_plugins(cls):
        return list(cls._registry.keys())

# Plugins auto-register
class JSONPlugin(Plugin, name="json"):
    def serialize(self, data):
        import json
        return json.dumps(data)

class XMLPlugin(Plugin, name="xml"):
    def serialize(self, data):
        # XML serialization
        pass

class CSVPlugin(Plugin, name="csv"):
    def serialize(self, data):
        # CSV serialization
        pass

# Usage
print(Plugin.list_plugins())  # ["json", "xml", "csv"]

plugin = Plugin.get_plugin("json")()
print(plugin.serialize({"key": "value"}))
```

**Benefits:**
- No manual registration.
- New plugins just subclass.
- Clean, maintainable code.

Python: What is the __init_subclass__ for plugin registration?