gh-84995: Run sys.__interactivehook__() on asyncio REPL startup (#20517)

This makes the asyncio REPL (`python -m asyncio`) more usable
and similar to the regular REPL.

This exposes register_readline() as a top-level function in site.py,
but it's intentionally undocumented. 

Co-authored-by: Carol Willing <carolcode@willingconsulting.com>
Co-authored-by: Itamar Oren <itamarost@gmail.com>

Lib/asyncio/__main__.py

@@ -3,6 +3,7 @@ import asyncio
 import code
 import concurrent.futures
 import inspect
+import site
 import sys
 import threading
 import types
@@ -109,6 +110,21 @@ if __name__ == '__main__':
     except ImportError:
         pass
 
+    interactive_hook = getattr(sys, "__interactivehook__", None)
+
+    if interactive_hook is not None:
+        interactive_hook()
+
+    if interactive_hook is site.register_readline:
+        # Fix the completer function to use the interactive console locals
+        try:
+            import rlcompleter
+        except:
+            pass
+        else:
+            completer = rlcompleter.Completer(console.locals)
+            readline.set_completer(completer.complete)
+
     repl_thread = REPLThread()
     repl_thread.daemon = True
     repl_thread.start()

Lib/site.py

@@ -460,13 +460,18 @@ def gethistoryfile():
 def enablerlcompleter():
     """Enable default readline configuration on interactive prompts, by
     registering a sys.__interactivehook__.
+    """
+    sys.__interactivehook__ = register_readline
+
+
+def register_readline():
+    """Configure readline completion on interactive prompts.
 
     If the readline module can be imported, the hook will set the Tab key
     as completion key and register ~/.python_history as history file.
     This can be overridden in the sitecustomize or usercustomize module,
     or in a PYTHONSTARTUP file.
     """
-    def register_readline():
     import atexit
     try:
         import readline
@@ -506,14 +511,13 @@ def enablerlcompleter():
         def write_history():
             try:
                 readline.write_history_file(history)
-                except OSError:
-                    # bpo-19891, bpo-41193: Home directory does not exist
-                    # or is not writable, or the filesystem is read-only.
+            except (FileNotFoundError, PermissionError):
+                # home directory does not exist or is not writable
+                # https://bugs.python.org/issue19891
                 pass
 
         atexit.register(write_history)
 
-    sys.__interactivehook__ = register_readline
 
 def venv(known_paths):
     global PREFIXES, ENABLE_USER_SITE

Misc/NEWS.d/next/Library/2020-05-29-18-08-54.bpo-40818.Ij8ffq.rst

@@ -0,0 +1,3 @@
+The asyncio REPL now runs :data:`sys.__interactivehook__` on startup. The
+default implementation of :data:`sys.__interactivehook__` provides
+auto-completion to the asyncio REPL. Patch contributed by Rémi Lapeyre.