bpo-36889: Merge asyncio streams (GH-13251)

https://bugs.python.org/issue36889

Author: asvetlov

Lib/asyncio/__init__.py

@@ -3,6 +3,7 @@
 # flake8: noqa
 
 import sys
+import warnings
 
 # This relies on each of the submodules having an __all__ variable.
 from .base_events import *
@@ -43,3 +44,40 @@
 else:
     from .unix_events import *  # pragma: no cover
     __all__ += unix_events.__all__
+
+
+__all__ += ('StreamReader', 'StreamWriter', 'StreamReaderProtocol')  # deprecated
+
+
+def __getattr__(name):
+    global StreamReader, StreamWriter, StreamReaderProtocol
+    if name == 'StreamReader':
+        warnings.warn("StreamReader is deprecated since Python 3.8 "
+                      "in favor of Stream, and scheduled for removal "
+                      "in Python 3.10",
+                      DeprecationWarning,
+                      stacklevel=2)
+        from .streams import StreamReader as sr
+        StreamReader = sr
+        return StreamReader
+    if name == 'StreamWriter':
+        warnings.warn("StreamWriter is deprecated since Python 3.8 "
+                      "in favor of Stream, and scheduled for removal "
+                      "in Python 3.10",
+                      DeprecationWarning,
+                      stacklevel=2)
+        from .streams import StreamWriter as sw
+        StreamWriter = sw
+        return StreamWriter
+    if name == 'StreamReaderProtocol':
+        warnings.warn("Using asyncio internal class StreamReaderProtocol "
+                      "is deprecated since Python 3.8 "
+                      " and scheduled for removal "
+                      "in Python 3.10",
+                      DeprecationWarning,
+                      stacklevel=2)
+        from .streams import StreamReaderProtocol as srp
+        StreamReaderProtocol = srp
+        return StreamReaderProtocol
+
+    raise AttributeError(f"module {__name__} has no attribute {name}")