complete draft: update from Atlas

15-more-types/cast/empty.py

@@ -0,0 +1,2 @@
+# Mypy 0.812 can't spot this inevitable runtime IndexError
+print([][0])

15-more-types/cast/find.py

@@ -0,0 +1,23 @@
+# tag::CAST[]
+from typing import cast
+
+def find_first_str(a: list[object]) -> str:
+    index = next(i for i, x in enumerate(a) if isinstance(x, str))
+    # We only get here if there's at least one string in a
+    return cast(str, a[index])
+# end::CAST[]
+
+
+from typing import TYPE_CHECKING
+
+l1 = [10, 20, 'thirty', 40]
+if TYPE_CHECKING:
+    reveal_type(l1)
+
+print(find_first_str(l1))
+
+l2 = [0, ()]
+try:
+    find_first_str(l2)
+except StopIteration as e:
+    print(repr(e))

15-more-types/cast/tcp_echo.py

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+import asyncio
+
+from asyncio import StreamReader, StreamWriter
+
+# tag::CAST_IMPORTS[]
+from asyncio.trsock import TransportSocket
+from typing import cast
+# end::CAST_IMPORTS[]
+
+async def handle_echo(reader: StreamReader, writer: StreamWriter) -> None:
+    data = await reader.read(100)
+    message = data.decode()
+    addr = writer.get_extra_info('peername')
+
+    print(f"Received {message!r} from {addr!r}")
+
+    print(f"Send: {message!r}")
+    writer.write(data)
+    await writer.drain()
+
+    print("Close the connection")
+    writer.close()
+
+async def main() -> None:
+    server = await asyncio.start_server(
+        handle_echo, '127.0.0.1', 8888)
+
+    # tag::CAST_USE[]
+    socket_list = cast(tuple[TransportSocket, ...], server.sockets)
+    addr = socket_list[0].getsockname()
+    # end::CAST_USE[]
+    print(f'Serving on {addr}')
+
+    async with server:
+        await server.serve_forever()
+
+asyncio.run(main())

15-more-types/cast/tcp_echo_no_cast.py

@@ -0,0 +1,29 @@
+import asyncio
+
+from asyncio import StreamReader, StreamWriter
+
+async def handle_echo(reader: StreamReader, writer: StreamWriter) -> None:
+    data = await reader.read(100)
+    message = data.decode()
+    addr = writer.get_extra_info('peername')
+
+    print(f"Received {message!r} from {addr!r}")
+
+    print(f"Send: {message!r}")
+    writer.write(data)
+    await writer.drain()
+
+    print("Close the connection")
+    writer.close()
+
+async def main() -> None:
+    server = await asyncio.start_server(
+        handle_echo, '127.0.0.1', 8888)
+
+    addr = server.sockets[0].getsockname()
+    print(f'Serving on {addr}')
+
+    async with server:
+        await server.serve_forever()
+
+asyncio.run(main())