Fixed issue #51: "Passing **kwargs to Template.__init__() modifies the context"

Also added a test case.

pystache/template.py

@@ -62,15 +62,22 @@ class Template(object):
     modifiers = Modifiers()
 
     def __init__(self, template=None, context=None, **kwargs):
+        """
+        The **kwargs arguments are only supported if the context is
+        a dictionary (i.e. not a View).
+
+        """
         from .view import View
 
         self.template = template
 
         if context is None:
             context = {}
-
-        if kwargs:
-            context.update(kwargs)
+        elif not isinstance(context, View):
+            # Views do not support copy() or update().
+            context = context.copy()
+            if kwargs:
+                context.update(kwargs)
 
         self.view = context if isinstance(context, View) else View(context=context)
         self._compile_regexps()

tests/test_template.py

@@ -12,6 +12,8 @@ from pystache.template import Template
 
 class TemplateTestCase(unittest.TestCase):
 
+    """Test the Template class."""
+
     def test_init__kwargs_with_no_context(self):
         """
         Test passing **kwargs with no context.
@@ -20,3 +22,12 @@ class TemplateTestCase(unittest.TestCase):
         # This test checks that the following line raises no exception.
         template = Template(foo="bar")
 
+    def test_init__kwargs_does_not_modify_context(self):
+        """
+        Test that passing **kwargs does not modify the passed context.
+
+        """
+        context = {}
+        template = Template(context=context, foo="bar")
+        self.assertEquals(context, {})
+