Add chapter_09 iterator pattern

patterns/chapter_09_iterator/__init__.py

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+"""Init file for chapter_09_iterator package."""

patterns/chapter_09_iterator/iterators.py

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+"""Custom iterator class."""
+
+from __future__ import annotations
+
+
+class Iterator:
+    """Iterator class."""
+
+    def __init__(self, collection: list[tuple[str, float]]) -> None:
+        """Initialize iterator."""
+        self._collection = collection
+        self._index = 0
+
+    def __iter__(self) -> Iterator:
+        """Return iterator."""
+        return self
+
+    def __next__(self) -> tuple[str, float]:
+        """Return next element."""
+        if self._index >= len(self._collection):
+            raise StopIteration
+        current_element = self._collection[self._index]
+        self._index += 1
+        return current_element

patterns/chapter_09_iterator/main.py

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+"""Iterator module."""
+
+from __future__ import annotations
+
+from .menus import DinerMenu, Menu, PancackeMenu
+from .waitress import Waitress
+
+
+def run_pattern_example() -> None:
+    """Run pattern example."""
+    pancake_menu: Menu = PancackeMenu()
+    diner_menu: Menu = DinerMenu()
+
+    pancake_menu.add_item({"pancake": 1.99})
+    pancake_menu.add_item({"waffle": 2.99})
+
+    diner_menu.add_item(("spaghetti", 3.99))
+    diner_menu.add_item(("meatballs", 4.99))
+
+    waitress: Waitress = Waitress([pancake_menu, diner_menu])
+    waitress.print_all_menus()
+
+
+if __name__ == "__main__":
+    run_pattern_example()

patterns/chapter_09_iterator/menus.py

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+"""Abstract Menu class and 2 implementations."""
+
+from abc import ABC, abstractmethod
+
+from .iterators import Iterator
+
+
+class Menu(ABC):
+    """Abstract Menu class."""
+
+    _description: str
+
+    @abstractmethod
+    def add_item(self, item) -> None:
+        """Add item to menu (abstract method).
+
+        All child classes must implement this method.
+        """
+        ...
+
+    @abstractmethod
+    def create_iterator(self) -> Iterator:
+        """Create iterator for menu items (abstract method).
+
+        All child classes must implement this method.
+        """
+        ...
+
+    @property
+    def description(self) -> str:
+        """Return menu description."""
+        return self._description
+
+
+class DinerMenu(Menu):
+    """Diner menu class.
+
+    Uses tuples to store menu items.
+    """
+
+    _description: str = 'Diner menu'
+
+    def __init__(self) -> None:
+        """Initialize menu."""
+        self._menu_items: list[tuple[str, float]] = []
+
+    def add_item(self, item: tuple[str, float]) -> None:
+        """Add item to menu."""
+        self._menu_items.append(item)
+
+    def create_iterator(self) -> Iterator:
+        """Create iterator for menu items."""
+        return Iterator(self._menu_items)
+
+
+class PancackeMenu(Menu):
+    """Pancake menu class.
+
+    Uses dict to store menu items.
+    """
+
+    _description = 'Pancake menu'
+
+    def __init__(self) -> None:
+        """Initialize menu."""
+        self._menu_items: dict[str, float] = {}
+
+    def add_item(self, item: dict[str, float]) -> None:
+        """Add item to menu."""
+        self._menu_items.update(item)
+
+    def create_iterator(self) -> Iterator:
+        """Create iterator for menu items."""
+        return Iterator(list(self._menu_items.items()))

patterns/chapter_09_iterator/waitress.py

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+"""Waitress class for printing menus."""
+
+from typing import Iterable, cast
+
+from .iterators import Iterator
+from .menus import Menu
+
+
+class Waitress:
+    """Waitress class."""
+
+    def __init__(self, menus: Iterable[Menu]) -> None:
+        """Initialize waitress with menus."""
+        self._menus = menus
+
+    def print_all_menus(self) -> None:
+        """Print all menus."""
+        for menu in self._menus:
+            print(menu.description)
+            iterator = menu.create_iterator()
+            self._print_menu(iterator)
+
+    def _print_menu(self, iterator: Iterator) -> None:
+        """Print one menu."""
+        for item, price, *_ in iterator:
+            print(f'- {cast(str, item)}: {price}')