Drop official support for Python versions before 3.8

This change does not modify any code, so the codebase is still actually
compatible with Python 2.7 through 3.7, but it gives the project the
freedom to make incompatible changes with versions in that range in
subsequent commits.

A note in the documentation states that compatibility with earlier
versions could be considered if there is user demand.

doc/index.rst

@@ -107,6 +107,15 @@ gives access to many of the documentation strings included in the code.
 Installation and download
 =========================
 
+Supported Python versions
+-------------------------
+
+The :mod:`uncertainties` package supports all versions of Python supported by
+the upstream Python_ project.  As of early 2024, that means versions 3.8
+through 3.12.  It may be possible to support earlier versions if there is user
+demand.  Versions of the :mod:`uncertainties` package up through 3.1.7
+supported Python 2.7 through Python 3.12.
+
 Important note
 --------------
 

setup.py

@@ -1,22 +1,9 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
-# !! This program must run with all version of Python since 2.3 included.
-
 import os
 import sys
 
-# setuptools has python_requires, but distutils doesn't, so we test the
-# Python version manually:
-min_version = (2, 7)
-error_msg = ("Sorry, this package is for Python %d.%d and higher only." %
-             min_version)
-try:
-    if sys.version_info < min_version:
-        sys.exit(error_msg)
-except AttributeError:  # sys.version_info was introduced in Python 2.0
-    sys.exit(error_msg)
-
 # Common options for distutils/setuptools's setup():
 setup_options = dict(
     name='uncertainties',
@@ -280,19 +267,12 @@
         'License :: OSI Approved :: BSD License',
         'Operating System :: OS Independent',
         'Programming Language :: Python',
-        'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
-        # Python 3.1 failed because of a problem with NumPy 1.6.1 (whereas
-        # everything was fine with Python 3.2 and Python 2.7).
-        'Programming Language :: Python :: 3.1',
-        'Programming Language :: Python :: 3.2',
-        'Programming Language :: Python :: 3.3',
-        'Programming Language :: Python :: 3.4',
-        'Programming Language :: Python :: 3.5',
-        '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',
+        'Programming Language :: Python :: 3.11',
+        'Programming Language :: Python :: 3.12',
         'Programming Language :: Python :: Implementation :: Jython',
         'Programming Language :: Python :: Implementation :: PyPy',
         'Topic :: Education',