Don't render an empty string when a tag's value is 0.

pystache/template.py

@@ -97,7 +97,10 @@ class Template(object):
     @modifier(None)
     def render_tag(self, tag_name, context):
         """Given a tag name and context, finds, escapes, and renders the tag."""
-        return cgi.escape(unicode(context.get(tag_name, '') or ''))
+        raw = context.get(tag_name, '')
+        if not raw and raw is not 0:
+            return ''
+        return cgi.escape(unicode(raw))
 
     @modifier('!')
     def render_comment(self, tag_name=None, context=None):

tests/test_pystache.py

@@ -27,6 +27,11 @@ class TestPystache(unittest.TestCase):
         ret = pystache.render(template, { 'name': 'Jon' })
         self.assertEquals(ret, "I think Jon wants a , right Jon?")
 
+    def test_render_zero(self):
+        template = 'My value is {{value}}.'
+        ret = pystache.render(template, { 'value': 0 })
+        self.assertEquals(ret, 'My value is 0.')
+
     def test_comments(self):
         template = "What {{! the }} what?"
         ret = pystache.render(template)