Fix bug 833666, "scour does not clean comments if file starts with a comment", by correctly and efficiently iterating over the elements of a live sequence. Unit tests are updated.

scour.py

@@ -2575,7 +2575,9 @@ def removeComments(element) :
 	if isinstance(element, xml.dom.minidom.Document):
 		# must process the document object separately, because its
 		# documentElement's nodes have None as their parentNode
-		for subelement in element.childNodes:
+		# iterate in reverse order to prevent mess-ups with renumbering
+		for index in xrange(len(element.childNodes) - 1, -1, -1):
+			subelement = element.childNodes[index]
 			if isinstance(subelement, xml.dom.minidom.Comment):
 				numCommentBytes += len(subelement.data)
 				element.removeChild(subelement)
@@ -2585,7 +2587,9 @@ def removeComments(element) :
 		numCommentBytes += len(element.data)
 		element.parentNode.removeChild(element)
 	else:
-		for subelement in element.childNodes:
+		# iterate in reverse order to prevent mess-ups with renumbering
+		for index in xrange(len(element.childNodes) - 1, -1, -1):
+			subelement = element.childNodes[index]
 			removeComments(subelement)
 
 def embedRasters(element, options) :

unittests/comment-beside-xml-decl.svg

@@ -1,4 +1,10 @@
 <?xml version="1.0" encoding="utf-8" standalone="yes"?>
 <!-- Oh look a comment -->
+<!-- generated by foobar version 20120503 -->
+<!-- And another -->
 <svg xmlns="http://www.w3.org/2000/svg">
+  <!-- This comment is meant to test whether removing a comment before <svg>
+       messes up removing comments thereafter -->
+  <!-- And this one is meant to test whether iteration works correctly in
+       <svg> as well as the document element -->
 </svg>