Support n filter in the page tag

doc/build/filtering.rst

@@ -169,6 +169,20 @@ will render ``myexpression`` with no filtering of any kind, and:
 
 will render ``myexpression`` using the ``trim`` filter only.
 
+Including the ``n`` filter in a ``<%page>`` tag will only disable
+``default_filters``. In effect this makes the filters from the tag replace
+default filters instead of adding to them. For example:
+
+.. sourcecode:: mako
+
+    <%page expression_filter="n, json.dumps"/>
+    data = {a: ${123}, b: ${"123"}};
+
+will suppress turning the values into strings using the default filter, so that
+``json.dumps`` (which requires ``imports=["import json"]`` or something
+equivalent) can take the value type into account, formatting numbers as numeric
+literals and strings as string literals.
+
 Filtering Defs and Blocks
 =========================
 

mako/codegen.py

@@ -802,7 +802,7 @@ def locate_encode(name):
             if is_expression:
                 if self.compiler.pagetag:
                     args = self.compiler.pagetag.filter_args.args + args
-                if self.compiler.default_filters:
+                if self.compiler.default_filters and "n" not in args:
                     args = self.compiler.default_filters + args
         for e in args:
             # if filter given as a function, get just the identifier portion

test/test_filters.py

@@ -294,6 +294,17 @@ def test_nflag(self):
         )
         assert t.render().strip() == "<tag>this is html</tag>"
 
+    def test_global_json(self):
+        t = Template(
+            """
+<%!
+import json
+%><%page expression_filter="n, json.dumps"/>
+data = {a: ${123}, b: ${"123"}};
+        """
+        )
+        assert t.render().strip() == """data = {a: 123, b: "123"};"""
+
     def test_non_expression(self):
         t = Template(
             """