Add __slots__ to stream classes

We use `__slots__` almost everywhere else in the codebase, however `__slots__`
were not implemented in stream

related issue #4618

aiohttp/streams.py

@@ -42,6 +42,9 @@ class EofStream(Exception):
 
 
 class AsyncStreamIterator(Generic[_T]):
+
+    __slots__ = ("read_func",)
+
     def __init__(self, read_func: Callable[[], Awaitable[_T]]) -> None:
         self.read_func = read_func
 
@@ -59,6 +62,9 @@ async def __anext__(self) -> _T:
 
 
 class ChunkTupleAsyncStreamIterator:
+
+    __slots__ = ("_stream",)
+
     def __init__(self, stream: "StreamReader") -> None:
         self._stream = stream
 
@@ -107,6 +113,25 @@ class StreamReader(AsyncStreamReaderMixin):
 
     """
 
+    __slots__ = (
+        "_protocol",
+        "_low_water",
+        "_high_water",
+        "_loop",
+        "_size",
+        "_cursor",
+        "_http_chunk_splits",
+        "_buffer",
+        "_buffer_offset",
+        "_eof",
+        "_waiter",
+        "_eof_waiter",
+        "_exception",
+        "_timer",
+        "_eof_callbacks",
+        "total_bytes",
+    )
+
     total_bytes = 0
 
     def __init__(
@@ -505,6 +530,9 @@ def _read_nowait(self, n: int) -> bytes:
 
 
 class EmptyStreamReader(StreamReader):  # lgtm [py/missing-call-to-init]
+
+    __slots__ = ("_read_eof_chunk",)
+
     def __init__(self) -> None:
         self._read_eof_chunk = False
 
@@ -573,6 +601,15 @@ def read_nowait(self, n: int = -1) -> bytes:
 class DataQueue(Generic[_SizedT]):
     """DataQueue is a general-purpose blocking queue with one reader."""
 
+    __slots__ = (
+        "_loop",
+        "_eof",
+        "_waiter",
+        "_exception",
+        "_size",
+        "_buffer",
+    )
+
     def __init__(self, loop: asyncio.AbstractEventLoop) -> None:
         self._loop = loop
         self._eof = False
@@ -653,6 +690,8 @@ class FlowControlDataQueue(DataQueue[_SizedT]):
     It is a destination for parsed data.
     """
 
+    __slots__ = ("_protocol", "_limit")
+
     def __init__(
         self, protocol: BaseProtocol, limit: int, *, loop: asyncio.AbstractEventLoop
     ) -> None: