require python 3.6

* HACKING, NEWS, README, doc/org/install.org: Update.
* m4/pypath.m4, python/spot/__init__.py: Adjust requirements.
* python/spot/ltsmin.i: Don't use capture_output, this is a 3.7
option.

HACKING

@@ -42,7 +42,7 @@ since the generated files they produce are distributed.)
   A complete LaTeX distribution, including latexmk and extra fonts
     like dsfont.sty.
   ImageMagick
-  Python >= 3.5, IPython >= 2.3
+  Python >= 3.6, IPython >= 2.3
   Jupyter >= 4, with nbconvert
   GraphViz
   Java >= 1.7 (needed to run PlantUML while generating the doc)

NEWS

@@ -1,5 +1,11 @@
 New in spot 2.11.6.dev  (not yet released)
 
+  Build:
+
+  - When Python bindings are enabled, Spot now requires Python 3.6 or
+    later.  Python 3.6 has reached end-of-life in 2021, but is still
+    used on CentOS 7 (which will reach end-of-support later in 2024).
+
   Documentation:
 
   - https://spot.lre.epita.fr/tut25.html is a new example showing

README

@@ -76,7 +76,7 @@ Requirements
 Spot requires a C++17-compliant compiler.  G++ 7.x or later, as well
 as Clang++ 5.0 or later should work.
 
-Spot expects a complete installation of Python (version 3.5 or later).
+Spot expects a complete installation of Python (version 3.6 or later).
 Especially, Python's headers files should be installed.  If you don't
 have Python installed, and do NOT want to install it, you should run
 configure with the --disable-python option (see below).
@@ -133,7 +133,7 @@ flags specific to Spot:
     offers a convenient interface when used in an IPython notebook,
     and are also used to build the CGI script that translates LTL
     formulas on-line.  You may safely disable these, especially if you
-    do not have a working Python 3.2+ installation or if you are
+    do not have a working Python 3.6+ installation or if you are
     attempting some cross-compilation.
 
   --enable-max-accsets=N

doc/org/install.org

@@ -22,7 +22,7 @@ successful development build]].
 Spot requires a C++17-compliant compiler.  =g++= 7.0 or later, as well
 as =clang++= 5.0 or later should work.
 
-Spot expects a complete installation of Python (version 3.5 or later).
+Spot expects a complete installation of Python (version 3.6 or later).
 Especially, Python's headers files should be installed (the package to
 install has a name like =python-dev= or =libpython3-dev= in most
 distributions).  If you don't have Python installed, and do NOT want

m4/pypath.m4

@@ -1,5 +1,5 @@
 AC_DEFUN([adl_CHECK_PYTHON],
- [AM_PATH_PYTHON([3.5])
+ [AM_PATH_PYTHON([3.6])
   case $PYTHON in
     [[\\/$]]* | ?:[[\\/]]* );;
     *) AC_MSG_ERROR([The PYTHON variable must be set to an absolute filename.]);;

python/spot/__init__.py

@@ -19,8 +19,8 @@
 
 import sys
 
-if sys.hexversion < 0x03030000:
-    sys.exit("This module requires Python 3.3 or newer")
+if sys.hexversion < 0x03060000:
+    sys.exit("This module requires Python 3.6 or newer")
 
 import subprocess
 import os
@@ -710,7 +710,7 @@ def automata(*sources, timeout=None, ignore_abort=True,
             # returned by spot.automata() is destroyed.  Otherwise, _supress()
             # is just a dummy context manager that does nothing (Python 3.7
             # introduces nullcontext() for this purpose, but at the time of
-            # writing we support Python 3.4).
+            # writing we still have to support Python 3.6).
             mgr = proc if proc else _supress()
             with mgr:
                 while a:
@@ -730,7 +730,7 @@ def automata(*sources, timeout=None, ignore_abort=True,
                 # an exception.
                 if ret and sys.exc_info()[0] is None:
                     raise subprocess.CalledProcessError(ret, filename[:-1])
-    # deleting o explicitly now prevents Python 3.5 from
+    # deleting o explicitly used to prevent Python 3.5 from
     # reporting the following error: "<built-in function
     # delete_automaton_parser_options> returned a result with
     # an error set".  It's not clear to me if the bug is in Python

python/spot/ltsmin.i

@@ -173,7 +173,8 @@ try:
                    try:
                        p = subprocess.run(['divine', 'compile',
                                              '--ltsmin', t.name],
-                                            capture_output=True,
+                                            stdout=subprocess.PIPE,
+                                            stderr=subprocess.PIPE,
                                             universal_newlines=True)
                        if p.stdout: print(p.stdout)
                        if p.stderr: print(p.stderr, file=sys.stderr)