Add chapter_11 proxy pattern

patterns/chapter_11_proxy/__init__.py

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+"""Init file for chapter_11_proxy package."""

patterns/chapter_11_proxy/main.py

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+"""Proxy Pattern example module."""
+
+import asyncio
+
+from .remote_images import Proxy, RemoteImage
+
+
+async def run_pattern_example() -> None:
+    """Run proxy example.
+
+    While remote image is downloaded, proxy displays fake image.
+    """
+    remote_image = RemoteImage()
+    proxy = Proxy(remote_image)
+
+    task1 = asyncio.create_task(remote_image.download())
+    task2 = asyncio.create_task(proxy.display())
+
+    await task1
+    await task2
+
+
+if __name__ == "__main__":
+    asyncio.run(run_pattern_example())

patterns/chapter_11_proxy/remote_images.py

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+"""Abstract Remote Image Interface, it's implementation and proxy."""
+import asyncio
+from abc import ABC, abstractmethod
+
+DOWNLOAD_DELAY = 2
+REFRESH_RATE = 0.5
+
+
+class AbstractRemoteImage(ABC):
+    """Abstract Remote Image Interface."""
+
+    @abstractmethod
+    async def display(self):
+        """Abstract display method.
+
+        All child classes should implement this method.
+        """
+        pass
+
+
+class RemoteImage(AbstractRemoteImage):
+    """Remote Image class."""
+
+    def __init__(self) -> None:
+        """Initialize Remote Image.
+
+        It's not downloaded by default.
+        """
+        self._is_downloaded = False
+
+    async def download(self):
+        """Download the image."""
+        await asyncio.sleep(DOWNLOAD_DELAY)
+        self._is_downloaded = True
+
+    async def display(self):
+        """Display the downloaded image."""
+        print('Displaying the downloaded image.')
+
+    @property
+    def is_downloaded(self) -> bool:
+        """Check if the image is downloaded."""
+        return self._is_downloaded
+
+
+class Proxy(AbstractRemoteImage):
+    """Proxy class for Remote Image."""
+
+    def __init__(self, remote_image: RemoteImage) -> None:
+        """Initialize Proxy."""
+        self._remote_image = remote_image
+
+    async def display(self):
+        """Display the image.
+
+        Displays the fake image while the real image is downloading.
+        """
+        while not self._remote_image.is_downloaded:
+            print('Displaying the fake image.')
+            await asyncio.sleep(REFRESH_RATE)
+        await self._remote_image.display()