Add GatheringTaskGroup class for Python 3.10 and below (#52)

* Add GatheringTaskGroup class for Python 3.10 and below

* Fix issues

* results() should not be async

* More fixes

* Update changelog

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Next version
+
+- [#52](https://github.com/sdss/sdsstools/pull/52) Add basic support for `GatheringTaskGroup` for Python versions 3.10 and below.
+
 ## [1.8.1](https://github.com/sdss/sdsstools/compare/1.8.0...1.8.1)
 
 - Fixed import of `GatheringTaskGroup` for Python < 3.11.

src/sdsstools/utils.py

@@ -23,6 +23,7 @@
     "get_temporary_file_path",
     "run_in_executor",
     "cancel_task",
+    "GatheringTaskGroup",
 ]
 
 
@@ -139,4 +140,50 @@ def results(self):
 
             return [task.result() for task in self.__tasks]
 
+else:
+
+    class GatheringTaskGroup:
+        """Simple implementation of ``asyncio.TaskGroup`` for Python 3.10 and below.
+
+        The behaviour of this class is not exactly the same as ``asyncio.TaskGroup``,
+        especially when it comes to handling of exceptions during execution.
+
+        """
+
+        def __init__(self):
+            self._tasks = []
+            self._joined: bool = False
+
+        def __repr__(self):
+            return f"<GatheringTaskGroup tasks={len(self._tasks)}>"
+
+        async def __aenter__(self):
+            self._joined = False
+            self._tasks = []
+
+            return self
+
+        async def __aexit__(self, exc_type, exc_value, traceback):
+            if exc_type is not None:
+                return False
+
+            await asyncio.gather(*self._tasks)
+            self._joined = True
+
+        def create_task(self, coro):
+            """Creates a task and appends it to the list of tasks."""
+
+            task = asyncio.create_task(coro)
+            self._tasks.append(task)
+
+            return task
+
+        def results(self):
+            """Returns the results of the tasks in the same order they were created."""
+
+            if not self._joined:
+                raise RuntimeError("Tasks have not been gathered yet.")
+
+            return [task.result() for task in self._tasks]
+
     __all__.append("GatheringTaskGroup")

test/test_utils.py

@@ -9,24 +9,20 @@
 from __future__ import annotations
 
 import asyncio
-import sys
 import warnings
 from time import sleep
 
 import pytest
 
 from sdsstools.utils import (
+    GatheringTaskGroup,
     Timer,
     cancel_task,
     get_temporary_file_path,
     run_in_executor,
 )
 
 
-if sys.version_info >= (3, 11):
-    from sdsstools.utils import GatheringTaskGroup
-
-
 def test_timer():
     with Timer() as timer:
         sleep(0.1)
@@ -101,7 +97,6 @@ async def test_cancel_task_None():
     await cancel_task(task)
 
 
-@pytest.mark.skipif(sys.version_info < (3, 11), reason="requires python3.11 or higher")
 async def test_gathering_task_group():
     async def _task(i):
         await asyncio.sleep(0.1)
@@ -114,7 +109,6 @@ async def _task(i):
     assert group.results() == list(range(10))
 
 
-@pytest.mark.skipif(sys.version_info < (3, 11), reason="requires python3.11 or higher")
 async def test_gathering_task_group_results_fails():
     async def _task(i):
         await asyncio.sleep(0.1)