diff --git a/code/newsletter/N4/switcher.py b/code/newsletter/N4/switcher.py
new file mode 100644
index 0000000..4ceed89
--- /dev/null
+++ b/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()
diff --git a/code/newsletter/N4/threadpool_simulation.py b/code/newsletter/N4/threadpool_simulation.py
new file mode 100644
index 0000000..6cc3a3f
--- /dev/null
+++ b/code/newsletter/N4/threadpool_simulation.py
@@ -0,0 +1,33 @@
+import contextlib
+
+
+class Thread:
+    def __init__(self, max_worker):
+        self.max_worker = max_worker
+
+    def execute(self, func, *args, **kwargs):
+        print(f"Using {self.max_worker} workers to execute {func.__name__} function...")
+        func(*args, **kwargs)
+
+
+@contextlib.contextmanager
+def ThreadPoolExecutor(max_worker=1):
+    pool = Thread(max_worker)
+    print("Initial for threads...")
+    try:
+        yield pool
+    finally:
+        print("Recycling threads and closing pool...")
+
+
+def echo(s):
+    print(f"\techo: {s}")
+
+
+def main():
+    with ThreadPoolExecutor(max_worker=2) as pool:
+        pool.execute(echo, s="Hello, world!")
+
+
+if __name__ == '__main__':
+    main()