make parameter parser work with python3

Tools/px4params/srcparser.py

@@ -57,10 +57,10 @@ class Parameter(object):
 
     def GetType(self):
         return self.type
-    
+
     def GetDefault(self):
         return self.default
-    
+
     def SetField(self, code, value):
         """
         Set named field value
@@ -80,6 +80,10 @@ class Parameter(object):
         """
         Return value of the given field code or None if not found.
         """
+        fv =  self.fields.get(code)
+        if not fv:
+                # required because python 3 sorted does not accept None
+                return ""
         return self.fields.get(code)
 
 class SourceParser(object):
@@ -89,7 +93,7 @@ class SourceParser(object):
 
     re_split_lines = re.compile(r'[\r\n]+')
     re_comment_start = re.compile(r'^\/\*\*')
-    re_comment_content = re.compile(r'^\*\s*(.*)') 
+    re_comment_content = re.compile(r'^\*\s*(.*)')
     re_comment_tag = re.compile(r'@([a-zA-Z][a-zA-Z0-9_]*)\s*(.*)')
     re_comment_end = re.compile(r'(.*?)\s*\*\/')
     re_parameter_definition = re.compile(r'PARAM_DEFINE_([A-Z_][A-Z0-9_]*)\s*\(([A-Z_][A-Z0-9_]*)\s*,\s*([^ ,\)]+)\s*\)\s*;')

Tools/px4params/xmlout.py

@@ -52,5 +52,4 @@ class XMLOutput():
         self.xml_document = ET.ElementTree(xml_parameters)
 
     def Save(self, filename):
-        with codecs.open(filename, 'w', 'utf-8') as f:
-            self.xml_document.write(f)
+        self.xml_document.write(filename, encoding="UTF-8")

makefiles/firmware.mk

@@ -494,7 +494,7 @@ $(filter %.S.o,$(OBJS)): $(WORK_DIR)%.S.o: %.S $(GLOBAL_DEPS)
 $(PRODUCT_BUNDLE):	$(PRODUCT_BIN)
 	@$(ECHO) %% Generating $@
 ifdef GEN_PARAM_XML
-	python $(PX4_BASE)/Tools/px_process_params.py --src-path $(PX4_BASE)/src --board CONFIG_ARCH_BOARD_$(CONFIG_BOARD) --xml
+	$(Q) $(PYTHON) $(PX4_BASE)/Tools/px_process_params.py --src-path $(PX4_BASE)/src --board CONFIG_ARCH_BOARD_$(CONFIG_BOARD) --xml
 	$(Q) $(MKFW) --prototype $(IMAGE_DIR)/$(BOARD).prototype \
 		--git_identity $(PX4_BASE) \
 		--parameter_xml $(PRODUCT_PARAMXML) \