Python example solution Gilded Rose code Kata to http://codingdojo.org/kata/GildedRose/

gilded_rose.py

import logging
import inspect
from dataclasses import dataclass, field
from typing import List, ClassVar

import pytest

logging.basicConfig(level=logging.DEBUG)
logger = logging.getLogger('rose')


class ItemRegistry:
    registry = {}

    @staticmethod
    def register(item_category, cls):
        ItemRegistry.registry[item_category] = cls

    @staticmethod
    def get_class(item_category):
        # Default to using Item if name is unknown
        return ItemRegistry.registry.get(item_category, Item)

@dataclass
class Item:
    category: str
    quality: int = 10
    sell_in: int = 1

    def update_quality(self):
        "Daily quality change"
        if self.quality > 0:
            if self.sell_in >= 0:
                self.quality -= 1
            else:
                self.quality -= 2

    def update_sell_in(self):
        "Daily sell-in change"
        self.sell_in -= 1

    def max_quality(self):
        if self.quality > 50:
            self.quality = 50

    RULES = ['update_sell_in', 'update_quality', 'max_quality']

    @staticmethod
    def make(category, *args, **kwargs):
        """
        Instantiate the correct class of Item for the given category
        """
        return ItemRegistry.get_class(category)(category, *args, **kwargs)

    def update(self):
        """
        Apply all rules to this instance
        """
        logger.debug("%s %s", id(self), self)
        for rule_name in self.RULES:
            # Look up rule name on self and call it
            getattr(self, rule_name)()
            logger.debug("%s %s %s", id(self), rule_name, self)

def named_item(cls):
    "Class decorator to register a known item type"
    # Register this class so our make factory method knows it
    ItemRegistry.register(cls.DEFINED_CATEGORY, cls)

@named_item
class Sulfuras(Item):
    DEFINED_CATEGORY = 'Sulfuras'

    def update_quality(self):
        pass  # Sulfuras doesn't go bad

    def update_sell_in(self):
        pass  # Sulfuras doesn't sell

@named_item
class AgedBrie(Item):
    DEFINED_CATEGORY = 'Aged Brie'

    def update_quality(self):
        "Daily quality change"
        self.quality += 1  # Brie increases in quality with age

@named_item
class BackstagePass(Item):
    DEFINED_CATEGORY = 'Backstage Pass'

    def update_quality(self):
        "Daily quality change"
        if self.sell_in < 0:
            self.quality = 0
        elif self.sell_in <= 5:
            self.quality += 3
        elif self.sell_in <= 10:
            self.quality += 2
        else:
            self.quality += 1

@named_item
class Conjured(Item):
    DEFINED_CATEGORY = 'Conjured'

    def update_quality(self):
        "Daily quality change"
        if self.quality > 0:
            if self.sell_in >= 0:
                self.quality -= 2
            else:
                self.quality -= 4


def test_no_negative_quality():
    i = Item.make('test', quality=1); i.update(); assert i.quality == 0
    i = Item.make('test', quality=0); i.update(); assert i.quality == 0

def test_quality_suffers_after_sell():
    i = Item.make('test', quality=4, sell_in=2); i.update(); assert i.quality == 3
    i = Item.make('test', quality=4, sell_in=-1); i.update(); assert i.quality == 2

def test_brie_quality_increases():
    i = Item.make('Aged Brie', quality=4, sell_in=2); i.update(); assert i.quality == 5

def test_max_quality():
    i = Item.make('Aged Brie', quality=50, sell_in=2); i.update(); assert i.quality == 50

def test_sulfuras():
    i = Item.make('Sulfuras', quality=1, sell_in=1); i.update()
    assert i.quality == 1
    assert i.sell_in == 1

def test_backstage_pass():
    i = Item.make('Backstage Pass', quality=10, sell_in=12); i.update(); assert i.quality == 11
    i = Item.make('Backstage Pass', quality=10, sell_in=11); i.update(); assert i.quality == 12
    i = Item.make('Backstage Pass', quality=10, sell_in=6); i.update(); assert i.quality == 13
    i = Item.make('Backstage Pass', quality=10, sell_in=0); i.update(); assert i.quality == 0

def test_conjured():
    i = Item.make('Conjured', quality=10, sell_in=12); i.update(); assert i.quality == 8
    i = Item.make('Conjured', quality=10, sell_in=0); i.update(); assert i.quality == 6

if __name__=='__main__':
    # print(ItemRegistry.registry)
    pytest.main(['gilded_rose.py', '-v'])