ENH: support simultaneously python2 and python3

Modules/Wrappers/SWIG/otb-module-init.cmake

@@ -19,9 +19,10 @@
 #
 
 option ( OTB_WRAP_PYTHON "Wrap Python" OFF )
+option ( OTB_WRAP_PYTHON3 "Wrap Python 3" OFF )
 option ( OTB_WRAP_JAVA   "Wrap Java"   OFF )
 
-if ( OTB_WRAP_PYTHON OR OTB_WRAP_JAVA )
+if ( OTB_WRAP_PYTHON OR OTB_WRAP_JAVA OR OTB_WRAP_PYTHON3)
   find_package ( SWIG REQUIRED )
   mark_as_advanced(SWIG_DIR)
   mark_as_advanced(SWIG_EXECUTABLE)
@@ -43,11 +44,61 @@ endmacro()
 
 if ( OTB_WRAP_PYTHON )
   check_PIC_flag ( Python )
-  find_package ( PythonLibs REQUIRED )
   find_package ( PythonInterp REQUIRED )
+  find_package ( PythonLibs REQUIRED )
   find_package ( Numpy )
 endif()
 
+macro(swap_cache_variable var1 var2)
+  set(_backup ${${var1}})
+  get_property(_var1_type CACHE ${var1} PROPERTY TYPE)
+  get_property(_var1_help CACHE ${var1} PROPERTY HELPSTRING)
+  get_property(_var2_type CACHE ${var2} PROPERTY TYPE)
+  get_property(_var2_help CACHE ${var2} PROPERTY HELPSTRING)
+  set(${var1} ${${var2}} CACHE ${_var1_type} "${_var1_help}" FORCE)
+  set(${var2} ${_backup} CACHE ${_var2_type} "${_var2_help}" FORCE)
+endmacro()
+
+macro(swap_variable var1 var2)
+  set(_backup ${${var1}})
+  set(${var1} ${${var2}})
+  set(${var2} ${_backup})
+endmacro()
+
+if ( OTB_WRAP_PYTHON3 )
+  set(PYTHON3_EXECUTABLE "PYTHON3_EXECUTABLE-NOTFOUND" CACHE FILEPATH "Path to python 3 interpreter")
+  set(PYTHON3_INCLUDE_DIR "PYTHON3_INCLUDE_DIR-NOTFOUND" CACHE PATH "Path to python 3 include directory")
+  set(PYTHON3_LIBRARY "PYTHON3_LIBRARY-NOTFOUND" CACHE FILEPATH "Path to python 3 library")
+  set(PYTHON3_LIBRARY_DEBUG "PYTHON3_LIBRARY_DEBUG-NOTFOUND" CACHE FILEPATH "Path to python 3 library (debug)")
+  set(PYTHON3_LIBRARY_RELEASE "PYTHON3_LIBRARY_RELEASE-NOTFOUND" CACHE FILEPATH "Path to python 3 library (release)")
+  set(NUMPY_PYTHON3_INCLUDE_DIR "NUMPY_PYTHON3_INCLUDE_DIR" CACHE PATH "Path to numpy module for Python 3")
+
+  # Swap cache variables between python and python3
+  swap_cache_variable(PYTHON_EXECUTABLE PYTHON3_EXECUTABLE)
+  swap_cache_variable(PYTHON_INCLUDE_DIR PYTHON3_INCLUDE_DIR)
+  swap_cache_variable(PYTHON_LIBRARY PYTHON3_LIBRARY)
+  swap_cache_variable(PYTHON_LIBRARY_DEBUG PYTHON3_LIBRARY_DEBUG)
+  swap_cache_variable(PYTHON_LIBRARY_RELEASE PYTHON3_LIBRARY_RELEASE)
+  swap_cache_variable(NUMPY_INCLUDE_DIR NUMPY_PYTHON3_INCLUDE_DIR)
+
+  swap_variable(PYTHON_LIBRARIES PYTHON3_LIBRARIES)
+
+  check_PIC_flag ( Python )
+  find_package ( PythonInterp 3 REQUIRED )
+  find_package ( PythonLibs 3 REQUIRED )
+  find_package ( Numpy )
+
+  # Swap cache variables between python and python3
+  swap_cache_variable(PYTHON_EXECUTABLE PYTHON3_EXECUTABLE)
+  swap_cache_variable(PYTHON_INCLUDE_DIR PYTHON3_INCLUDE_DIR)
+  swap_cache_variable(PYTHON_LIBRARY PYTHON3_LIBRARY)
+  swap_cache_variable(PYTHON_LIBRARY_DEBUG PYTHON3_LIBRARY_DEBUG)
+  swap_cache_variable(PYTHON_LIBRARY_RELEASE PYTHON3_LIBRARY_RELEASE)
+  swap_cache_variable(NUMPY_INCLUDE_DIR NUMPY_PYTHON3_INCLUDE_DIR)
+
+  swap_variable(PYTHON_LIBRARIES PYTHON3_LIBRARIES)
+endif()
+
 #
 # JAVA SWIG configuration
 #