Add 'shortcuts' module.

ppp_libmodule/shortcuts.py

@@ -0,0 +1,22 @@
+from .simplification import simplify
+
+from ppp_datamodel.communication import TraceItem, Response
+
+
+def traverse_until_fixpoint(predicate, tree):
+    """Traverses the tree again and again until it is not modified."""
+    old_tree = None
+    tree = simplify(tree)
+    while tree and old_tree != tree:
+        old_tree = tree
+        tree = tree.traverse(predicate)
+        if not tree:
+            return None
+        tree = simplify(tree)
+    return tree
+
+
+def build_answer(request, tree, measures, module_name):
+    trace = request.trace + [TraceItem(module_name, tree, measures)]
+    return Response(request.language, tree, measures, trace)
+

tests/test_shortcuts.py

@@ -0,0 +1,45 @@
+from ppp_libmodule.tests import PPPTestCase
+from ppp_libmodule.http import HttpRequestHandler
+from ppp_libmodule import shortcuts
+
+from ppp_datamodel.nodes import Triple as T
+from ppp_datamodel.nodes import Missing as M
+from ppp_datamodel.nodes import Missing as R
+from ppp_datamodel.communication import Response, TraceItem
+
+def predicate(node):
+    if node == T(M(), M(), M()):
+        return R('foo')
+    elif node == R('foo'):
+        return R('bar')
+    elif node == M():
+        return node
+    else:
+        assert False, node
+
+class RequestHandler:
+    def __init__(self, request):
+        self.request = request
+
+    def answer(self):
+        tree = self.request.tree.traverse(predicate)
+        if tree != self.request.tree:
+            # If we have modified the tree, it is relevant to return it
+            return [shortcuts.build_answer(self.request, tree, {}, 'test')]
+        else:
+            # Otherwise, we have nothing interesting to say.
+            return []
+
+def app(environ, start_response):
+    """Function called by the WSGI server."""
+    r = HttpRequestHandler(environ, start_response, RequestHandler).dispatch()
+    return r
+
+class HttpTest(PPPTestCase(app)):
+    def testWorking(self):
+        t = T(M(), M(), M())
+        q = {'id': '1', 'language': 'en', 'tree': t.as_dict(),
+              'measures': {}, 'trace': []}
+        self.assertResponse(q, [Response('en', R('bar'), {},
+            [TraceItem('test', R('bar'), {})])])
+