Trac #30053: Python 3.7+: setlocale: LC_ALL: cannot change locale (C.…

…UTF-8) from build/bin/sage-spkg and in doctests; disable use of system Python 3.6

In #29033 in `build/bin/sage-spkg` LC_ALL was changed to C.UTF-8
However, not all systems have it.

See also:
 - #22659

Follow-up:
 - #30586 macOS: Doctest failures in some locales
 - #30576 Python 3.6: Fix locale/encoding issues, then re-enable Python
3.6

URL: https://trac.sagemath.org/30053
Reported by: dimpase
Ticket author(s): Dima Pasechnik, Matthias Koeppe
Reviewer(s): Matthias Koeppe, Dima Pasechnik

build/bin/sage-spkg

@@ -69,8 +69,10 @@
 
 # Avoid surprises with character ranges [a-z] in regular expressions
 # See Trac #15791; some locales can produce different results for
-# character ranges (use C.UTF-8 to ensure UTF-8 default encoding in Python)
-export LC_ALL=C.UTF-8
+# character ranges; using C.UTF-8 to ensure UTF-8 default encoding in Python
+# introduces extra complications, see #30053, so we don't do it, but
+# assume we are on Python3.x,  for x at least 7.
+export LC_ALL=C
 
 usage()
 {

build/pkgs/python3/spkg-configure.m4

@@ -10,14 +10,14 @@ SAGE_SPKG_CONFIGURE([python3], [
         dnl Using Python 3 for Sage.  Check if we can do venv with a system python3
         dnl instead of building our own copy.
         check_modules="sqlite3, ctypes, math, hashlib, crypt, readline, socket, zlib, distutils.core"
-        AC_CACHE_CHECK([for python3 >= 3.6, < 3.9 with modules $check_modules], [ac_cv_path_PYTHON3], [
+        AC_CACHE_CHECK([for python3 >= 3.7, < 3.9 with modules $check_modules], [ac_cv_path_PYTHON3], [
             AC_MSG_RESULT([])
-            AC_PATH_PROGS_FEATURE_CHECK([PYTHON3], [python3.8 python3.7 python3.6 python3], [
+            AC_PATH_PROGS_FEATURE_CHECK([PYTHON3], [python3.8 python3.7 python3], [
                 AC_MSG_CHECKING([... whether $ac_path_PYTHON3 is good])
                 python3_version=`"$ac_path_PYTHON3" --version 2>&1 \
                     | $SED -n -e 's/\([[0-9]]*\.[[0-9]]*\.[[0-9]]*\).*/\1/p'`
                 AS_IF([test -n "$python3_version"], [
-                    AX_COMPARE_VERSION([$python3_version], [ge], [3.6.0], [
+                    AX_COMPARE_VERSION([$python3_version], [ge], [3.7.0], [
                         AX_COMPARE_VERSION([$python3_version], [lt], [3.9.0], [
                             dnl Because the system python is not used directly but rather in a venv without site-packages,
                             dnl we test whether the module will be available in a venv.