Drop support for python version 3.6

Python version 3.6 was supported until December 23-rd 2021
(see https://endoflife.date/python) meaning its end of life has expired
before more than 20 days.
Dropping support for python version 3.6 will allow us to make some
small cleanups.

python-tuf dropped support for python3.6 as well:
theupdateframework/python-tuf#1783

Signed-off-by: Martin Vrachev <mvrachev@vmware.com>

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
  fail-fast: false
  # Run tests on each OS/Python combination
  matrix:
- python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"]
+ python-version: ["3.7", "3.8", "3.9", "3.10"]
  # TODO: Add windows-latest when gpg issues are solved
  os: [ubuntu-latest, macos-latest]
  toxenv: [py]

requirements.txt

@@ -16,7 +16,7 @@
 # 1. Use this script to create a pinned requirements file for each Python
 # version
 # ```
-# for v in 3.6 3.7 3.8 3.9; do
+# for v in 3.7 3.8 3.9; do
 # mkvirtualenv sslib-env-${v} -p python${v};
 # pip install pip-tools;
 # pip-compile --no-header -o requirements-${v}.txt requirements.txt;

setup.py

@@ -88,7 +88,6 @@
  'Operating System :: MacOS :: MacOS X',
  'Operating System :: Microsoft :: Windows',
  'Programming Language :: Python :: 3',
- 'Programming Language :: Python :: 3.6',
  'Programming Language :: Python :: 3.7',
  'Programming Language :: Python :: 3.8',
  'Programming Language :: Python :: 3.9',
@@ -101,7 +100,7 @@
  'Source': 'https://github.com/secure-systems-lab/securesystemslib',
  'Issues': 'https://github.com/secure-systems-lab/securesystemslib/issues',
  },
- python_requires = "~=3.6",
+ python_requires = "~=3.7",
  extras_require = {
  'colors': ['colorama>=0.3.9'],
  'crypto': ['cryptography>=3.3.2'],

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = mypy, py36, py37, py38, py39, py310, purepy38, py38-no-gpg
+envlist = mypy, py37, py38, py39, py310, purepy38, py38-no-gpg
 skipsdist = True
 
 [testenv]