Drop Python 3.6 support

Python 3.6 has been EOL since December 23, 2021.  Drop support.

Debian stable has 3.9 and Ubuntu 20.04 LTS has 3.8. Ubuntu 18.04 LTS has
3.6, but there's been a newer LTS version for over a year.  The default
Python 3 in RHEL 8 is 3.6, but newer versions are available in AppStreams.

Fixes #161.

Author: bgilbert

.github/workflows/python.yml

@@ -28,7 +28,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        python-version: [3.6, 3.7, 3.8, 3.9, "3.10"]
+        python-version: [3.7, 3.8, 3.9, "3.10"]
     steps:
     - name: Check out repo
       uses: actions/checkout@v2
@@ -71,7 +71,7 @@ jobs:
         shell: bash
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9, "3.10"]
+        python-version: [3.7, 3.8, 3.9, "3.10"]
         python-arch: [x86, x64]
     steps:
     - name: Check out repo

.pre-commit-config.yaml

@@ -18,7 +18,7 @@ repos:
     hooks:
       - id: pyupgrade
         name: Modernize python code
-        args: ["--py36-plus"]
+        args: ["--py37-plus"]
 
   - repo: https://github.com/PyCQA/isort
     rev: 5.8.0

README.md

@@ -37,7 +37,7 @@ OpenSlide can read virtual slides in several formats:
 
 ## Requirements
 
-* Python ≥ 3.6
+* Python ≥ 3.7
 * OpenSlide ≥ 3.4.0
 * Pillow
 

setup.py

@@ -39,14 +39,13 @@
         'Operating System :: POSIX :: Linux',
         'Programming Language :: Python',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3.10',
         'Topic :: Scientific/Engineering :: Bio-Informatics',
     ],
-    python_requires='>=3.6',
+    python_requires='>=3.7',
     install_requires=[
         'Pillow',
     ],