Modify ThreadedHistory example(s) for new API

Author: Bob Hyman

examples/prompts/history/slow-history.py

@@ -5,6 +5,7 @@
 By wrapping it in `ThreadedHistory`, the history will load in the background
 without blocking any user interaction.
 """
+import asyncio
 import time
 
 from prompt_toolkit import PromptSession
@@ -32,11 +33,22 @@ def main():
         "Even when the input is accepted, loading will continue in the "
         "background and when the next prompt is displayed.\n"
     )
-    our_history = ThreadedHistory(SlowHistory())
+
+    my_loop = asyncio.get_event_loop()  # creates loop if needed
+
+    # Inform ThreadedHistory which event loop to use
+    # when passing lines of history to the prompt.
+
+    our_history = ThreadedHistory(SlowHistory(), my_loop)
 
     # The history needs to be passed to the `PromptSession`. It can't be passed
     # to the `prompt` call because only one history can be used during a
     # session.
+    # Note that PromptSession runs on the thread's current event loop because
+    # it was created above and is therefore in synch with ThreadedHistory.
+    # PromptSession would create and event loop if it didn't find one
+    # already running, but then ThreadedHistory would not work.
+
     session = PromptSession(history=our_history)
 
     while True:

prompt_toolkit/history.py

@@ -10,10 +10,10 @@
 import datetime
 import os
 import time
+import warnings
 from abc import ABCMeta, abstractmethod
 from threading import Thread
 from typing import Callable, Iterable, List, Optional
-import warnings
 
 __all__ = [
     "History",
@@ -40,7 +40,10 @@ def __init__(self) -> None:
     # Methods expected by `Buffer`.
     #
 
-    def load(self, item_loaded_callback: Callable[[str], None],) -> None:
+    def load(
+        self,
+        item_loaded_callback: Callable[[str], None],
+    ) -> None:
         """
         Load the history and call the callback for every entry in the history.
         This one assumes the callback is only called from same thread as `Buffer` is using.
@@ -103,13 +106,13 @@ class ThreadedHistory(History):
     """
 
     def __init__(
-        self, history: History, event_loop: asyncio.BaseEventLoop = None
+        self, history: History, event_loop: Optional[asyncio.AbstractEventLoop] = None
     ) -> None:
         """Create instance of ThreadedHistory
 
         Args:
             history (History): Instance of History intended to run on a background thread.
-            event_loop (asyncio.BaseEventLoop, optional): The event loop on which prompt toolkit is running.
+            event_loop (asyncio.AbstractEventLoop, optional): The event loop on which prompt toolkit is running.
             (Deprecated) Defaults to ``asyncio.get_event_loop(), which may *create* the event loop. Caller should provide an explicit value.
         """
         self.history = history
@@ -151,7 +154,10 @@ def call_all_callbacks(item: str) -> None:
             self._load_thread.daemon = True
             self._load_thread.start()
 
-    def bg_loader(self, item_loaded_callback: Callable[[str], None],) -> None:
+    def bg_loader(
+        self,
+        item_loaded_callback: Callable[[str], None],
+    ) -> None:
         """
         Load the history and schedule the callback for every entry in the history.
         TODO: extend the callback so it can take a batch of lines in one event_loop dispatch.

prompt_toolkit/shortcuts/prompt.py

@@ -556,8 +556,7 @@ def display_placeholder() -> bool:
             # Users can insert processors here.
             DynamicProcessor(lambda: merge_processors(self.input_processors or [])),
             ConditionalProcessor(
-                AfterInput(lambda: self.placeholder),
-                filter=display_placeholder,
+                AfterInput(lambda: self.placeholder), filter=display_placeholder,
             ),
         ]