Remove support for Python 3.6

Ubuntu 20.04 with Python 3.8 has been supported for a while. Meanwhile,
Python 3.6 was released about five years ago, and is nearing the end of
official support.

.github/CONTRIBUTING.md

@@ -19,7 +19,7 @@ We get around Python flexible type system in several ways:
 * we are fairly verbose with naming, trying to help the reader with following the types;
 * we follow our type annotation system for method and function docstrings (planning to switch to [PEP 484](https://www.python.org/dev/peps/pep-0484/)); see later for the format.
 
-We support Python 3 only, requiring at least version 3.6.
+We support Python 3 only, requiring at least version 3.8.
 
 # Docstring type annotation format
 

.github/workflows/main.yml

@@ -7,11 +7,6 @@ on:
 jobs:
   test:
     runs-on: ubuntu-20.04
-    strategy:
-      matrix:
-        python-version:
-          - 3.8
-          - 3.6
 
     services:
       postgres:
@@ -31,10 +26,9 @@ jobs:
         with:
           submodules: true
 
-      - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v2
+      - uses: actions/setup-python@v2
         with:
-          python-version: ${{ matrix.python-version }}
+          python-version: 3.8
 
       - name: Install dependencies
         run: >-

docs/Installation.rst

@@ -16,7 +16,7 @@ These are our requirements (in particular we highlight those that are not usuall
 
 * `GNU compiler collection <https://gcc.gnu.org/>`_ (in particular the C compiler ``gcc``);
 
-* `Python <http://www.python.org/>`_ >= 3.6;
+* `Python <http://www.python.org/>`_ >= 3.8;
 
 * `libcg <http://libcg.sourceforge.net/>`_;
 

setup.py

@@ -202,7 +202,6 @@ def run(self):
         "Development Status :: 5 - Production/Stable",
         "Natural Language :: English",
         "Operating System :: POSIX :: Linux",
-        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.8",
         "License :: OSI Approved :: "
         "GNU Affero General Public License v3",