fix: Keep Python 3.6 support

setup.cfg

@@ -55,9 +55,9 @@ test =
     codecov
 dev =
 lint =
-    flake8>=3.7.9
+    flake8>=3.8.4
 typecheck =
-    mypy>=0.770
+    mypy>=0.790
 docs =
     sphinx
     sphinx-autodoc-typehints

src/aiotools/compat.py

@@ -11,3 +11,9 @@
     all_tasks = asyncio.all_tasks
 else:
     all_tasks = asyncio.Task.all_tasks
+
+
+if hasattr(asyncio, 'current_task'):
+    current_task = asyncio.current_task
+else:
+    current_task = asyncio.Task.current_task

src/aiotools/taskgroup.py

@@ -25,12 +25,18 @@
 from __future__ import annotations
 
 import asyncio
-from contextvars import ContextVar
+try:
+    from contextvars import ContextVar
+    has_contextvars = True
+except ImportError:
+    has_contextvars = False
 import functools
 import itertools
 import textwrap
 import traceback
 
+from .compat import current_task, get_running_loop
+
 
 __all__ = (
     'MultiError',
@@ -40,7 +46,8 @@
 )
 
 
-current_taskgroup: ContextVar[TaskGroup] = ContextVar('current_taskgroup')
+if has_contextvars:
+    current_taskgroup: ContextVar[TaskGroup] = ContextVar('current_taskgroup')
 
 
 class TaskGroup:
@@ -61,7 +68,7 @@ def __init__(self, *, name=None):
         self._entered = False
         self._exiting = False
         self._aborting = False
-        self._loop = None
+        self._loop = get_running_loop()
         self._parent_task = None
         self._parent_cancel_requested = False
         self._tasks = set()
@@ -94,19 +101,14 @@ async def __aenter__(self):
                 f"TaskGroup {self!r} has been already entered")
         self._entered = True
 
-        if self._loop is None:
-            self._loop = asyncio.get_event_loop()
-
-        if hasattr(asyncio, 'current_task'):
-            self._parent_task = asyncio.current_task(self._loop)
-        else:
-            self._parent_task = asyncio.Task.current_task(self._loop)
+        self._parent_task = current_task()
 
         if self._parent_task is None:
             raise RuntimeError(
                 f'TaskGroup {self!r} cannot determine the parent task')
         self._patch_task(self._parent_task)
-        self._current_taskgroup_token = current_taskgroup.set(self)
+        if has_contextvars:
+            self._current_taskgroup_token = current_taskgroup.set(self)
         return self
 
     async def __aexit__(self, et, exc, tb):
@@ -171,7 +173,8 @@ async def __aexit__(self, et, exc, tb):
 
         assert self._unfinished_tasks == 0
         self._on_completed_fut = None  # no longer needed
-        current_taskgroup.reset(self._current_taskgroup_token)
+        if has_contextvars:
+            current_taskgroup.reset(self._current_taskgroup_token)
 
         if self._base_error is not None:
             raise self._base_error

tests/test_taskgroup.py

@@ -1,4 +1,5 @@
 import asyncio
+import sys
 
 import pytest
 
@@ -26,6 +27,10 @@ async def test_delayed_subtasks():
 
 
 @pytest.mark.asyncio
+@pytest.mark.skipif(
+    sys.version_info < (3, 7),
+    reason='contextvars is available only in Python 3.7 or later',
+)
 async def test_contextual_taskgroup():
 
     refs = []
@@ -50,6 +55,10 @@ async def check_tg(delay):
             current_taskgroup.get()
 
 
+@pytest.mark.skipif(
+    sys.version_info < (3, 7),
+    reason='contextvars is available only in Python 3.7 or later',
+)
 @pytest.mark.filterwarnings('ignore::RuntimeWarning')
 @pytest.mark.asyncio
 async def test_contextual_taskgroup_spawning():