Replace 3.6 builds with 3.9

.github/workflows/python-package.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.6.9' , 3.7, 3.8]
+        python-version: [3.7, 3.8, 3.9]
         numpy_version: ['==1.16.4', '']
     services:
       redis:

setup.py

@@ -33,7 +33,7 @@
             'ipytree',
         ],
     },
-    python_requires='>=3.6, <4',
+    python_requires='>=3.7, <4',
     install_requires=dependencies,
     package_dir={'': '.'},
     packages=['zarr', 'zarr.tests'],
@@ -47,7 +47,6 @@
         'Topic :: Software Development :: Libraries :: Python Modules',
         'Operating System :: Unix',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py36, py37-npy{115,116,latest}, py38, docs
+envlist = py37-npy{115,116,latest}, py38, py39, docs
 
 [testenv]
 install_command = pip install --no-binary=numcodecs {opts} {packages}
@@ -18,13 +18,13 @@ commands =
     # clear out any data files generated during tests
     python -c 'import glob; import shutil; import os; [(shutil.rmtree(d) if os.path.isdir(d) else os.remove(d) if os.path.isfile(d) else None) for d in glob.glob("./example*")]'
     # main unit test runner
-    py36,py38: pytest -v --cov=zarr --cov-config=.coveragerc zarr
+    py38,py39: pytest -v --cov=zarr --cov-config=.coveragerc zarr
     # don't collect coverage when running older numpy versions
     py37-{npy115,npy116}: pytest -v zarr
     # collect coverage and run doctests under py37
     py37-npylatest: pytest -v --cov=zarr --cov-config=.coveragerc --doctest-plus zarr --remote-data
     # generate a coverage report
-    py36,py37-npylatest,py38: coverage report -m
+    py37-npylatest,py38,py39: coverage report -m
     # run doctests in the tutorial and spec
     py38: python -m doctest -o NORMALIZE_WHITESPACE -o ELLIPSIS docs/tutorial.rst docs/spec/v2.rst
     # pep8 checks
@@ -34,12 +34,12 @@ commands =
 deps =
     py37-npy115: numpy==1.15.4
     py37-npy116: numpy==1.16.4
-    py36,py37-npylatest,py38: -rrequirements_dev_numpy.txt
+    py37-npylatest,py38,py39: -rrequirements_dev_numpy.txt
     -rrequirements_dev_minimal.txt
     -rrequirements_dev_optional.txt
 
 [testenv:docs]
-basepython = python3.6
+basepython = python3.7
 changedir = docs
 deps =
     -rrequirements_rtfd.txt