Ensure ParamRef resolves synchronous generators asynchronously (#6885)

panel/chat/feed.py

@@ -26,6 +26,7 @@
 from ..layout.card import Card
 from ..layout.spacer import VSpacer
 from ..pane.image import SVG
+from ..util import to_async_gen
 from .icon import ChatReactionIcons
 from .message import ChatMessage
 
@@ -477,31 +478,14 @@ async def _schedule_placeholder(
                 return
             await asyncio.sleep(0.1)
 
-    async def _to_async_gen(self, sync_gen):
-        done = object()
-
-        def safe_next():
-            # Converts StopIteration to a sentinel value to avoid:
-            # TypeError: StopIteration interacts badly with generators and cannot be raised into a Future
-            try:
-                return next(sync_gen)
-            except StopIteration:
-                return done
-
-        while True:
-            value = await asyncio.to_thread(safe_next)
-            if value is done:
-                break
-            yield value
-
     async def _handle_callback(self, message, loop: asyncio.BaseEventLoop):
         callback_args = self._gather_callback_args(message)
         if iscoroutinefunction(self.callback):
             response = await self.callback(*callback_args)
         elif isasyncgenfunction(self.callback):
             response = self.callback(*callback_args)
         elif isgeneratorfunction(self.callback):
-            response = self._to_async_gen(self.callback(*callback_args))
+            response = to_async_gen(self.callback(*callback_args))
             # printing type(response) -> <class 'async_generator'>
         else:
             response = await asyncio.to_thread(self.callback, *callback_args)

panel/param.py

@@ -54,7 +54,7 @@ class Skip(RuntimeError):
 from .reactive import Reactive
 from .util import (
     abbreviated_repr, flatten, full_groupby, fullpath, is_parameterized,
-    param_name, recursive_parameterized,
+    param_name, recursive_parameterized, to_async_gen,
 )
 from .util.checks import is_dataframe, is_mpl_axes, is_series
 from .viewable import Layoutable, Viewable
@@ -887,19 +887,11 @@ def _replace_pane(self, *args, force=False):
                         param.DEBUG, 'Skip event was raised, skipping update.'
                     )
                     return
+            if isinstance(new_object, Generator):
+                new_object = to_async_gen(new_object)
             if inspect.isawaitable(new_object) or isinstance(new_object, types.AsyncGeneratorType):
                 param.parameterized.async_executor(partial(self._eval_async, new_object))
                 return
-            elif isinstance(new_object, Generator):
-                append_mode = self.generator_mode == 'append'
-                if append_mode:
-                    self._inner_layout[:] = []
-                for new_obj in new_object:
-                    if append_mode:
-                        self._inner_layout.append(new_obj)
-                        self._pane = self._inner_layout[-1]
-                    else:
-                        self._update_inner(new_obj)
             else:
                 self._update_inner(new_object)
         finally:

panel/tests/test_param.py

@@ -24,7 +24,9 @@
 from panel.param import (
     JSONInit, Param, ParamFunction, ParamMethod, Skip,
 )
-from panel.tests.util import mpl_available, mpl_figure
+from panel.tests.util import (
+    async_wait_until, mpl_available, mpl_figure, wait_until,
+)
 from panel.widgets import (
     AutocompleteInput, Button, Checkbox, DatePicker, DatetimeInput,
     EditableFloatSlider, EditableRangeSlider, LiteralInput, NumberInput,
@@ -1789,11 +1791,11 @@ def function(value):
 
     root = pane.get_root(document, comm)
 
-    assert root.children[0].text == '<p>False</p>\n'
+    wait_until(lambda: root.children[0].text == '<p>False</p>\n')
 
     checkbox.value = True
 
-    assert root.children[0].text == '<p>True</p>\n'
+    wait_until(lambda: root.children[0].text == '<p>True</p>\n')
 
 
 def test_param_generator_append(document, comm):
@@ -1807,15 +1809,17 @@ def function(value):
 
     root = pane.get_root(document, comm)
 
-    assert len(root.children) == 2
+    wait_until(lambda: len(root.children) == 2)
     assert root.children[0].text == '<p>False</p>\n'
     assert root.children[1].text == '<p>True</p>\n'
 
     checkbox.value = True
 
-    assert len(root.children) == 2
-    assert root.children[0].text == '<p>True</p>\n'
-    assert root.children[1].text == '<p>False</p>\n'
+    wait_until(lambda: len(root.children) == 2)
+    wait_until(lambda: (
+        (root.children[0].text == '<p>True</p>\n') and
+        (root.children[1].text == '<p>False</p>\n')
+    ))
 
 async def test_param_async_generator(document, comm):
     checkbox = Checkbox(value=False)
@@ -1827,15 +1831,11 @@ async def function(value):
 
     root = pane.get_root(document, comm)
 
-    await asyncio.sleep(0.01)
-
-    assert root.children[0].text == '<p>False</p>\n'
+    await async_wait_until(lambda: root.children[0].text == '<p>False</p>\n')
 
     checkbox.value = True
 
-    await asyncio.sleep(0.01)
-
-    assert root.children[0].text == '<p>True</p>\n'
+    await async_wait_until(lambda: root.children[0].text == '<p>True</p>\n')
 
 async def test_param_async_generator_append(document, comm):
     checkbox = Checkbox(value=False)
@@ -1849,21 +1849,17 @@ async def function(value):
 
     root = pane.get_root(document, comm)
 
-    await asyncio.sleep(0.01)
-    assert len(root.children) == 1
-    assert root.children[0].text == '<p>False</p>\n'
-    await asyncio.sleep(0.01)
-    assert len(root.children) == 2
+    await async_wait_until(lambda: len(root.children) == 1, interval=10)
+    await async_wait_until(lambda: root.children[0].text == '<p>False</p>\n')
+    await async_wait_until(lambda: len(root.children) == 2, interval=10)
     assert root.children[0].text == '<p>False</p>\n'
     assert root.children[1].text == '<p>True</p>\n'
 
     checkbox.value = True
 
-    await asyncio.sleep(0.01)
-    assert len(root.children) == 1
+    await async_wait_until(lambda: len(root.children) == 1, interval=10)
     assert root.children[0].text == '<p>True</p>\n'
-    await asyncio.sleep(0.01)
-    assert len(root.children) == 2
+    await async_wait_until(lambda: len(root.children) == 2, interval=10)
     assert root.children[0].text == '<p>True</p>\n'
     assert root.children[1].text == '<p>False</p>\n'
 
@@ -1879,11 +1875,11 @@ def function(value):
 
     root = pane.get_root(document, comm)
 
-    assert root.children[0].text == '<p>True</p>\n'
+    wait_until(lambda: root.children[0].text == '<p>True</p>\n')
 
     checkbox.value = True
 
-    assert root.children[0].text == '<p>False</p>\n'
+    wait_until(lambda: root.children[0].text == '<p>False</p>\n')
 
 async def test_param_async_generator_multiple(document, comm):
     checkbox = Checkbox(value=False)

panel/util/__init__.py

@@ -4,6 +4,7 @@
 from __future__ import annotations
 
 import ast
+import asyncio
 import base64
 import datetime as dt
 import json
@@ -484,3 +485,21 @@ def try_datetime64_to_datetime(value):
     if isinstance(value, np.datetime64):
         value = value.astype('datetime64[ms]').astype(datetime)
     return value
+
+
+async def to_async_gen(sync_gen):
+    done = object()
+
+    def safe_next():
+        # Converts StopIteration to a sentinel value to avoid:
+        # TypeError: StopIteration interacts badly with generators and cannot be raised into a Future
+        try:
+            return next(sync_gen)
+        except StopIteration:
+            return done
+
+    while True:
+        value = await asyncio.to_thread(safe_next)
+        if value is done:
+            break
+        yield value