Added proper scoping for local variables.

I chose semantics that make all variables defined in outer scopes
(including globals) visible as locals, unless overridden by assignment
in inner scope.

lib/python/TAL/DummyEngine.py

@@ -93,12 +93,21 @@ from TALVisitor import NAME_RE
 class DummyEngine:
 
     def __init__(self):
-        self.locals = {}
-        self.globals = {}
+        dict = {}
+        self.locals = self.globals = dict
+        self.stack = [dict]
 
-    # XXX scopes
+    def beginScope(self):
+        self.stack.append(self.locals)
+
+    def endScope(self):
+        assert len(self.stack) > 1, "more endScope() than beginScope() calls"
+        self.locals = self.stack.pop()
 
     def setLocal(self, name, value):
+        if self.locals is self.stack[-1]:
+            # Unmerge this scope's locals from previous scope of first set
+            self.locals = self.locals.copy()
         self.locals[name] = value
 
     def setGlobal(self, name, value):

lib/python/TAL/TALVisitor.py

@@ -110,8 +110,10 @@ class TALVisitor(CopyingDOMVisitor):
         self.engine = engine
 
     def visitElement(self, node):
+        self.engine.beginScope()
         if not self.checkTAL(node):
             CopyingDOMVisitor.visitElement(self, node)
+        self.engine.endScope()
 
     def checkTAL(self, node):
         # Do TAL expansion.  Return value is 1 if node expansion

lib/python/TAL/test/test3.xml

+<?xml version="1.0" ?>
+<p xmlns:z="http://xml.zope.org/namespaces/tal">
+  <span z:define="local x as str:hello brave new world">
+    <span z:insert="text local:x">outer variable x, first appearance</span>
+    <span z:define="local x as str:goodbye cruel world">
+      <span z:insert="text local:x">inner variable x</span>
+    </span>
+    <span z:insert="text local:x">outer variable x, second appearance</span>
+  </span>
+</p>

lib/python/TAL/tests/test3.xml

+<?xml version="1.0" ?>
+<p xmlns:z="http://xml.zope.org/namespaces/tal">
+  <span z:define="local x as str:hello brave new world">
+    <span z:insert="text local:x">outer variable x, first appearance</span>
+    <span z:define="local x as str:goodbye cruel world">
+      <span z:insert="text local:x">inner variable x</span>
+    </span>
+    <span z:insert="text local:x">outer variable x, second appearance</span>
+  </span>
+</p>