determine Python (3.10) version number correctly.

from upstream automake

configure

@@ -19594,7 +19594,7 @@ if test ${am_cv_python_version+y}
 then :
   printf %s "(cached) " >&6
 else $as_nop
-  am_cv_python_version=`$PYTHON -c "import sys; sys.stdout.write(sys.version[:3])"`
+  am_cv_python_version=`$PYTHON -c "import sys; print('%u.%u' % sys.version_info[:2])"`
 fi
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $am_cv_python_version" >&5
 printf "%s\n" "$am_cv_python_version" >&6; }

m4/python.m4

@@ -1,7 +1,7 @@
 ## ------------------------                                 -*- Autoconf -*-
 ## Python file handling
 ## From Andrew Dalke
-## Updated by James Henstridge
+## Updated by James Henstridge and other contributors.
 ## ------------------------
 # Copyright (C) 1999-2020 Free Software Foundation, Inc.
 #
@@ -86,12 +86,14 @@ AC_DEFUN([AM_PATH_PYTHON],
     m4_default([$3], [AC_MSG_ERROR([no suitable Python interpreter found])])
   else
 
-  dnl Query Python for its version number.  Getting [:3] seems to be
-  dnl the best way to do this; it's what "site.py" does in the standard
-  dnl library.
+  dnl Query Python for its version number.  Although site.py simply uses
+  dnl sys.version[:3], printing that failed with Python 3.10, since the
+  dnl trailing zero was eliminated. So now we output just the major
+  dnl and minor version numbers, as numbers. Apparently the tertiary
+  dnl version is not of interest.
 
   AC_CACHE_CHECK([for $am_display_PYTHON version], [am_cv_python_version],
-    [am_cv_python_version=`$PYTHON -c "import sys; sys.stdout.write(sys.version[[:3]])"`])
+    [am_cv_python_version=`$PYTHON -c "import sys; print('%u.%u' % sys.version_info[[:2]])"`])
   AC_SUBST([PYTHON_VERSION], [$am_cv_python_version])
 
   dnl Use the values of $prefix and $exec_prefix for the corresponding