feat: 新增技能拓展N4一章相关示例代码

code/newsletter/N4/switcher.py

@@ -0,0 +1,38 @@
+class Device:
+    def __init__(self, name: str):
+        self.name = name
+
+    def boot(self):
+        print(f"Device<{self.name}> is booting...")
+
+
+class Switcher:
+    def __init__(self) -> None:
+        pass
+
+    def __enter__(self):
+        self._on()
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        self._off()
+
+    def _on(self):
+        print(f"Loading switcher...")
+
+    def _off(self):
+        print(f"Closing switcher...")
+
+    def plug(self, device: Device):
+        device.boot()
+
+
+def main():
+
+    with Switcher() as switcher:
+        device = Device("PC")
+        switcher.plug(device)
+
+
+if __name__ == '__main__':
+    main()