Drop support for Python 3.6

.github/workflows/ci-windows.yaml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.6", "3.7", "3.8"]
+        python-version: ["3.7", "3.8"]
 
     steps:
       - name: Checkout source
@@ -23,13 +23,6 @@ jobs:
           activate-environment: dask-distributed
           auto-activate-base: false
 
-      - name: Install contextvars
-        shell: bash -l {0}
-        run: |
-          if [[ "${{ matrix.python-version }}" = "3.6" ]]; then
-            conda install -c conda-forge contextvars
-          fi
-
       - name: Install tornado
         shell: bash -l {0}
         run: |

.travis.yml

@@ -6,8 +6,7 @@ dist: trusty
 
 env:
   matrix:
-    - PYTHON=3.6 TESTS=true COVERAGE=true PACKAGES="lz4" TORNADO=5 CRICK=true
-    - PYTHON=3.7 TESTS=true PACKAGES="python-snappy python-blosc" TORNADO=6
+    - PYTHON=3.7 TESTS=true COVERAGE=true PACKAGES="lz4 python-snappy python-blosc" CRICK=true TORNADO=5
     - PYTHON=3.8 TESTS=true PACKAGES="python-snappy python-blosc" TORNADO=6
 
 matrix:

continuous_integration/travis/install.sh

@@ -67,10 +67,6 @@ conda create -n dask-distributed -c conda-forge -c defaults \
 
 source activate dask-distributed
 
-if [[ $PYTHON == 3.6 ]]; then
-  conda install -c conda-forge -c defaults contextvars
-fi
-
 if [[ $PYTHON == 3.8 ]]; then
     # Install pytorch to run related tests
     conda install -c pytorch -c conda-forge -c defaults pytorch torchvision

distributed/cli/tests/test_dask_scheduler.py

@@ -185,9 +185,6 @@ def test_interface(loop):
                 assert all("127.0.0.1" == d["host"] for d in info["workers"].values())
 
 
-@pytest.mark.skipif(
-    sys.version_info < (3, 7), reason="Intermittent failure on old Python version"
-)
 def test_pid_file(loop):
     def check_pidfile(proc, pidfile):
         start = time()

distributed/client.py

@@ -758,15 +758,6 @@ def as_current(self):
         method to return self. Any Future objects deserialized inside this context
         manager will be automatically attached to this Client.
         """
-        # In Python 3.6, contextvars are thread-local but not Task-local.
-        # We can still detect a race condition though.
-        if sys.version_info < (3, 7) and _current_client.get() not in (self, None):
-            raise RuntimeError(
-                "Detected race condition where multiple asynchronous clients tried "
-                "entering the as_current() context manager at the same time. "
-                "Please upgrade to Python 3.7+."
-            )
-
         tok = _current_client.set(self)
         try:
             yield

distributed/comm/tests/test_comms.py

@@ -222,8 +222,7 @@ async def handle_comm(comm):
     assert not handle_comm_called
 
     writer.close()
-    if hasattr(writer, "wait_closed"):  # always true for python >= 3.7, but not for 3.6
-        await writer.wait_closed()
+    await writer.wait_closed()
 
 
 @pytest.mark.asyncio

distributed/compatibility.py

@@ -10,16 +10,3 @@
 PYPY = platform.python_implementation().lower() == "pypy"
 WINDOWS = sys.platform.startswith("win")
 TORNADO6 = tornado.version_info[0] >= 6
-PY37 = sys.version_info[:2] >= (3, 7)
-
-if sys.version_info[:2] >= (3, 7):
-    from asyncio import get_running_loop
-else:
-
-    def get_running_loop():
-        from asyncio import _get_running_loop
-
-        loop = _get_running_loop()
-        if loop is None:
-            raise RuntimeError("no running event loop")
-        return loop

distributed/deploy/tests/test_local.py

@@ -1031,9 +1031,6 @@ async def test_capture_security(cleanup, temporary):
 
 
 @pytest.mark.asyncio
-@pytest.mark.skipif(
-    sys.version_info < (3, 7), reason="asyncio.all_tasks not implemented"
-)
 async def test_no_danglng_asyncio_tasks(cleanup):
     start = asyncio.all_tasks()
     async with LocalCluster(asynchronous=True, processes=False):

distributed/pubsub.py

@@ -1,6 +1,5 @@
 import asyncio
 from collections import defaultdict, deque
-from contextlib import suppress
 import logging
 import threading
 import weakref
@@ -421,8 +420,7 @@ async def _():
             try:
                 await asyncio.wait_for(_(), timeout2)
             finally:
-                with suppress(RuntimeError):  # Python 3.6 fails here sometimes
-                    self.condition.release()
+                self.condition.release()
 
         return self.buffer.popleft()
 

distributed/tests/test_client.py

@@ -3670,7 +3670,6 @@ async def test_reconnect_timeout(c, s):
 
 @pytest.mark.slow
 @pytest.mark.skipif(WINDOWS, reason="num_fds not supported on windows")
-@pytest.mark.skipif(sys.version_info < (3, 7), reason="TODO: intermittent failures")
 @pytest.mark.parametrize("worker,count,repeat", [(Worker, 100, 5), (Nanny, 10, 20)])
 def test_open_close_many_workers(loop, worker, count, repeat):
     psutil = pytest.importorskip("psutil")
@@ -4055,10 +4054,6 @@ def run2():
     t2.join()
 
 
-@pytest.mark.xfail(
-    sys.version_info < (3, 7),
-    reason="Python 3.6 contextvars are not copied on Task creation",
-)
 @gen_cluster(client=False)
 async def test_as_current_is_task_local(s, a, b):
     l1 = asyncio.Lock()

distributed/tests/test_core.py

@@ -1,7 +1,6 @@
 import asyncio
 import os
 import socket
-import sys
 import threading
 import weakref
 import warnings
@@ -209,10 +208,6 @@ class MyServer(Server):
     default_port = 8756
 
 
-@pytest.mark.skipif(
-    sys.version_info < (3, 7),
-    reason="asynccontextmanager not avaiable before Python 3.7",
-)
 @pytest.mark.asyncio
 async def test_server_listen():
     """

distributed/tests/test_diskutils.py

@@ -276,8 +276,6 @@ def _test_workspace_concurrency(tmpdir, timeout, max_procs):
 def test_workspace_concurrency(tmpdir):
     if WINDOWS:
         raise pytest.xfail.Exception("TODO: unknown failure on windows")
-    if sys.version_info < (3, 7):
-        raise pytest.xfail.Exception("TODO: unknown failure on Python 3.6")
     _test_workspace_concurrency(tmpdir, 5.0, 6)
 
 

distributed/tests/test_scheduler.py

@@ -1811,9 +1811,6 @@ async def test_get_task_duration(c, s, a, b):
 
 
 @pytest.mark.asyncio
-@pytest.mark.skipif(
-    sys.version_info < (3, 7), reason="asyncio.all_tasks not implemented"
-)
 async def test_no_danglng_asyncio_tasks(cleanup):
     start = asyncio.all_tasks()
     async with Scheduler(port=0) as s:

distributed/utils.py

@@ -55,7 +55,7 @@
 except ImportError:
     PollIOLoop = None  # dropped in tornado 6.0
 
-from .compatibility import PYPY, WINDOWS, get_running_loop
+from .compatibility import PYPY, WINDOWS
 from .metrics import time
 
 
@@ -1156,7 +1156,7 @@ def reset_logger_locks():
 
     if is_kernel():
         try:
-            get_running_loop()
+            asyncio.get_running_loop()
         except RuntimeError:
             is_kernel_and_no_running_loop = True
 

distributed/variable.py

@@ -89,8 +89,7 @@ async def _():  # Python 3.6 is odd and requires special help here
 
                 await asyncio.wait_for(_(), timeout=left)
             finally:
-                with suppress(RuntimeError):  # Python 3.6 loses lock on finally clause
-                    self.started.release()
+                self.started.release()
 
         record = self.variables[name]
         if record["type"] == "Future":

docs/source/install.rst

@@ -38,6 +38,6 @@ Notes
 <https://trac.macports.org/ticket/50058>`_.  with Python from macports that
 makes executables be placed in a location that is not available by default. A
 simple solution is to extend the ``PATH`` environment variable to the location
-where Python from macports install the binaries. For example, for Python 3.6::
+where Python from macports install the binaries. For example, for Python 3.7::
 
-    $ export PATH=/opt/local/Library/Frameworks/Python.framework/Versions/3.6/bin:$PATH
+    $ export PATH=/opt/local/Library/Frameworks/Python.framework/Versions/3.7/bin:$PATH

requirements.txt

@@ -1,6 +1,5 @@
 click >= 6.6
 cloudpickle >= 1.5.0
-contextvars;python_version<'3.7'
 dask>=2020.12.0
 msgpack >= 0.6.0
 psutil >= 5.0

setup.py

@@ -67,7 +67,7 @@
     url="https://distributed.dask.org",
     maintainer="Matthew Rocklin",
     maintainer_email="[email protected]",
-    python_requires=">=3.6",
+    python_requires=">=3.7",
     license="BSD",
     package_data={
         "": ["templates/index.html", "template.html"],
@@ -89,7 +89,6 @@
         "License :: OSI Approved :: BSD License",
         "Operating System :: OS Independent",
         "Programming Language :: Python",
-        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Topic :: Scientific/Engineering",