Remove need for Python 2to3

All Python examples and tests have been written to be both Python 2 and Python 3
compatible, removing the need for 2to3 to run the examples or test-suite.

The 2to3 executable is not always available and even when available does not
always work, e.g. with pyenv. An alternative would be to use the lib2to3 Python
module instead, but this isn't available in some older versions of Python 3.

I had this problem on Ubuntu Bionic on Travis:

  checking Examples/python/callback
  pyenv: 2to3-3.8: command not found
  The `2to3-3.8' command exists in these Python versions:
    3.8
    3.8.1

Reference issues:
  pypa/virtualenv#1399
  https://travis-ci.community/t/2to3-command-not-found-in-venv-in-bionic/4495

Author: wsfulton

CHANGES.current

@@ -7,6 +7,10 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.1.0 (in progress)
 ===========================
 
+2020-08-15: wsfulton
+            [Python] All Python examples and tests are written to be Python 2 and Python 3
+            compatible, removing the need for 2to3 to run the examples or test-suite.
+
 2020-08-13: wsfulton
             [C#] Add support for void *VOID_INT_PTR for member variables.
 

Examples/Makefile.in

@@ -381,13 +381,7 @@ python_static_cpp: $(SRCDIR_SRCS)
 # Running a Python example
 # -----------------------------------------------------------------
 
-ifeq (,$(PY3))
-  PYSCRIPT = $(RUNME).py
-else
-  PYSCRIPT = $(RUNME)3.py
-endif
-
-PY2TO3 = @PY2TO3@ `@PY2TO3@ -l | grep -v -E "Available|import$$" | awk '{print "-f "$$0}'`
+PYSCRIPT = $(RUNME).py
 
 python_run: $(PYSCRIPT)
 ifneq (,$(PYCODESTYLE))
@@ -400,10 +394,6 @@ $(RUNME).py: $(SRCDIR)$(RUNME).py
 	cp $< $@
 endif
 
-$(RUNME)3.py: $(SRCDIR)$(RUNME).py
-	cp $< $@
-	$(PY2TO3) -w $@ >/dev/null 2>&1
-
 # -----------------------------------------------------------------
 # Version display
 # -----------------------------------------------------------------
@@ -421,7 +411,6 @@ python_clean:
 	rm -f core @EXTRA_CLEAN@
 	rm -f *.@OBJEXT@ *@SO@ *$(PYTHON_SO)
 	rm -f $(TARGET).py
-	if test -f $(SRCDIR)$(RUNME).py; then rm -f $(RUNME)3.py $(RUNME)3.py.bak; fi
 	case "x$(SRCDIR)" in x|x./);; *) rm -f $(RUNME).py;; esac
 
 

Examples/python/index.html

@@ -89,7 +89,6 @@ <h2>Compilation Issues</h2>
 <h2>Compatibility</h2>
 
 For Python 3, set the environment variable <tt>PY3=1</tt>.
-This will ensure the 2to3 program is run prior to running any example.
 
 <p>
 Your mileage may vary.  If you experience a problem, please let us know by 

Examples/test-suite/python/Makefile.in

@@ -10,20 +10,10 @@ endif
 
 LANGUAGE     = python
 PYTHON       = $(PYBIN)
+SCRIPTSUFFIX = _runme.py
 PYCODESTYLE       = @PYCODESTYLE@
 PYCODESTYLE_FLAGS = --ignore=E252,E30,E402,E501,E731,E741,W291,W391
 
-#*_runme.py for Python 2.x, *_runme3.py for Python 3.x
-PY2SCRIPTSUFFIX = _runme.py
-PY3SCRIPTSUFFIX = _runme3.py
-PY2TO3       = @PY2TO3@ -x import
-
-ifeq (,$(PY3))
-  SCRIPTSUFFIX = $(PY2SCRIPTSUFFIX)
-else
-  SCRIPTSUFFIX = $(PY3SCRIPTSUFFIX)
-endif
-
 srcdir       = @srcdir@
 top_srcdir   = @top_srcdir@
 top_builddir = @top_builddir@
@@ -107,7 +97,6 @@ C_TEST_CASES += \
 include $(srcdir)/../common.mk
 
 # Overridden variables here
-SCRIPTDIR    = .
 LIBS         = -L.
 VALGRIND_OPT += --suppressions=pythonswig.supp
 
@@ -116,35 +105,25 @@ VALGRIND_OPT += --suppressions=pythonswig.supp
 
 # Rules for the different types of tests
 %.cpptest:
-	+$(convert_testcase)
 	$(setup)
 	+$(swig_and_compile_cpp)
 	$(check_pep8)
 	$(run_testcase)
 
 %.ctest:
-	+$(convert_testcase)
 	$(setup)
 	+$(swig_and_compile_c)
 	$(check_pep8)
 	$(run_testcase)
 
 %.multicpptest:
-	+$(convert_testcase)
 	$(setup)
 	+$(swig_and_compile_multi_cpp)
 	$(check_pep8_multi_cpp)
 	$(run_testcase)
 
 
-
-# Runs the testcase. A testcase is only run if
-# a file is found which has _runme.py (or _runme3.py for Python 3) appended after the testcase name.
-
-py_runme  = $(SCRIPTPREFIX)$*$(SCRIPTSUFFIX)
-py2_runme = $(SCRIPTPREFIX)$*$(PY2SCRIPTSUFFIX)
-py3_runme = $(SCRIPTPREFIX)$*$(PY3SCRIPTSUFFIX)
-
+# Python code style checking
 ifneq (,$(PYCODESTYLE))
 check_pep8 = $(COMPILETOOL) $(PYCODESTYLE) $(PYCODESTYLE_FLAGS) $(SCRIPTPREFIX)$*.py
 
@@ -154,70 +133,16 @@ check_pep8_multi_cpp = \
 	done
 endif
 
-run_python = env LD_LIBRARY_PATH=.:$$LD_LIBRARY_PATH PYTHONPATH=.:$(srcdir):$$PYTHONPATH $(RUNTOOL) $(PYTHON) $(py_runme)
-
+# Runs the testcase. A testcase is only run if
+# a file is found which has _runme.py appended after the testcase name.
 run_testcase = \
-	if [ -f $(SCRIPTDIR)/$(py_runme) ]; then \
-	  $(run_python);\
-	fi
-
-# Grab runme file ready for running: copied for out of source tree builds, and/or run 2to3
-# Note terminal (double colon) rules creating runme files to fix possible infinite recursion,
-# see https://github.com/swig/swig/pull/688
-ifeq ($(SCRIPTDIR),$(srcdir))
-  # in source tree build
-  ifeq (,$(PY3))
-    convert_testcase =
-  else
-    convert_testcase = \
-	if [ -f $(srcdir)/$(py2_runme) ]; then \
-	  $(MAKE) $(SCRIPTDIR)/$(py_runme); \
+	if [ -f $(SCRIPTDIR)/$(SCRIPTPREFIX)$*$(SCRIPTSUFFIX) ]; then \
+	  env LD_LIBRARY_PATH=.:$$LD_LIBRARY_PATH PYTHONPATH=.:$(srcdir):$$PYTHONPATH $(RUNTOOL) $(PYTHON) $(SCRIPTDIR)/$(SCRIPTPREFIX)$*$(SCRIPTSUFFIX); \
 	fi
 
-# For converting python 2 tests into Python 3 tests
-$(SCRIPTDIR)/$(SCRIPTPREFIX)%$(SCRIPTSUFFIX):: $(srcdir)/$(SCRIPTPREFIX)%$(PY2SCRIPTSUFFIX)
-	cp $< $@
-	$(PY2TO3) -w $@ >/dev/null 2>&1
-
-  endif
-else
-  # out of source tree build
-  ifeq (,$(PY3))
-    convert_testcase = \
-	if [ -f $(srcdir)/$(py2_runme) ]; then \
-	  $(MAKE) $(SCRIPTDIR)/$(py_runme); \
-	fi
-
-$(SCRIPTDIR)/$(SCRIPTPREFIX)%$(SCRIPTSUFFIX):: $(srcdir)/$(SCRIPTPREFIX)%$(PY2SCRIPTSUFFIX)
-	cp $< $@
-
-  else
-    convert_testcase = \
-	if [ -f $(srcdir)/$(py2_runme) ]; then \
-	  $(MAKE) $(SCRIPTDIR)/$(py_runme); \
-	elif [ -f $(srcdir)/$(py3_runme) ]; then \
-	  $(MAKE) $(SCRIPTDIR)/$(py3_runme); \
-	fi
-
-# For when there is a _runme3.py instead of a _runme.py, ie a Python 3 only run test
-$(SCRIPTDIR)/$(SCRIPTPREFIX)%$(SCRIPTSUFFIX):: $(srcdir)/$(SCRIPTPREFIX)%$(PY3SCRIPTSUFFIX)
-	cp $< $@
-
-# For converting python 2 tests into Python 3 tests
-$(SCRIPTDIR)/$(SCRIPTPREFIX)%$(SCRIPTSUFFIX):: $(srcdir)/$(SCRIPTPREFIX)%$(PY2SCRIPTSUFFIX)
-	cp $< $@
-	$(PY2TO3) -w $@ >/dev/null 2>&1
-
-  endif
-
-endif
-
 # Clean: remove the generated .py file
-# We only remove the _runme3.py if it is generated by 2to3 from a _runme.py.
 %.clean:
 	@rm -f $*.py
-	@if test -f $(srcdir)/$(py2_runme); then rm -f $(SCRIPTDIR)/$(py3_runme) $(SCRIPTDIR)/$(py3_runme).bak; fi
-	@if test "x$(SCRIPTDIR)" != "x$(srcdir)"; then rm -f $(SCRIPTDIR)/$(py_runme); fi
 
 clean:
 	$(MAKE) -f $(top_builddir)/$(EXAMPLES)/Makefile SRCDIR='$(SRCDIR)' python_clean

configure.ac

@@ -919,30 +919,6 @@ if test -n "$PYINCLUDE" || test -n "$PY3INCLUDE" ; then
   fi
 fi
 
-AC_ARG_WITH(2to3, AS_HELP_STRING([--with-2to3=path], [Set location of Python 2to3 tool]), [PY2TO3BIN="$withval"], [PY2TO3BIN="yes"])
-if test -n "$PYTHON3"; then
-  if test "x$PY2TO3BIN" = xyes; then
-    py3to2=`echo $PYTHON3 | sed -e "s/python/2to3-/"`
-    AC_CHECK_PROGS(PY2TO3, $py3to2 2to3)
-    if test -z "$PY2TO3"; then
-      # Windows distributions don't always have the 2to3 executable
-      AC_MSG_CHECKING(for 2to3.py)
-      py2to3script="$PY3PREFIX/Tools/scripts/2to3.py"
-      if test -f "$py2to3script"; then
-        AC_MSG_RESULT($py2to3script)
-        PY2TO3="$PYTHON3 $py2to3script"
-      else
-        AC_MSG_RESULT(Not found)
-      fi
-    fi
-  else
-    PY2TO3="$PY2TO3BIN"
-  fi
-  if test -z "$PY2TO3"; then
-    PYTHON3=
-  fi
-fi
-
 #----------------------------------------------------------------
 # Look for Perl5
 #----------------------------------------------------------------