Add string and nocall functions for Python expressions. Fixes #2.

CHANGES.rst

@@ -5,12 +5,15 @@
 3.1.0 (unreleased)
 ===================
 
-- Added support for Python 3.6.
-- Dropped support for Python 3.3.
+- Add support for Python 3.6.
+- Drop support for Python 3.3.
 - Use the adapter namespace from ``zope.pagetemplate`` if it's
   available, instead of the backwards compatibility shim in
   ``zope.app.pagetemplate``. See `issue 3
   <https://github.com/zopefoundation/z3c.pt/issues/3>`_.
+- Add the ``string`` and ``nocall`` functions for use inside Python
+  expressions. See `issue 2
+  <https://github.com/zopefoundation/z3c.pt/issues/2>`_.
 
 
 3.0 (2016-09-02)

src/z3c/pt/expressions.py

@@ -244,7 +244,7 @@ class PythonExpr(BasePythonExpr):
             tales=Builtin("tales"),
             name=ast.Str(s=name),
             mode="eval")
-        for name in ('path', 'exists')
+        for name in ('path', 'exists', 'string', 'nocall')
     }
 
     def __call__(self, target, engine):

src/z3c/pt/tests/test_templates.py

@@ -28,6 +28,26 @@ def setUp(self):
         import z3c.pt
         zope.configuration.xmlconfig.file('configure.zcml', z3c.pt)
 
+class TestPageTemplate(Setup,
+                       unittest.TestCase):
+
+    def test_string_function(self):
+        template = pagetemplate.PageTemplate('''<div tal:content="python:string('a string')" />''')
+        result = template.render()
+        self.assertEqual(result,
+                         '<div>a string</div>')
+
+    def test_nocall_function(self):
+        class Call(object):
+            def __call__(self):
+                raise AssertionError("Should not be called")
+            def __str__(self):
+                return "Not Called"
+        arg = {'call': Call()}
+        template = pagetemplate.PageTemplate('''<div tal:content="python:nocall('arg/call')" />''')
+        result = template.render(arg=arg)
+        self.assertEqual(result,
+                         '<div>Not Called</div>')
 
 class TestPageTemplateFile(Setup,
                            unittest.TestCase):