before_render_template signal

flask/__init__.py

@@ -34,7 +34,7 @@ from .templating import render_template, render_template_string
 from .signals import signals_available, template_rendered, request_started, \
      request_finished, got_request_exception, request_tearing_down, \
      appcontext_tearing_down, appcontext_pushed, \
-     appcontext_popped, message_flashed
+     appcontext_popped, message_flashed, before_render_template
 
 # We're not exposing the actual json module but a convenient wrapper around
 # it.

flask/signals.py

@@ -45,6 +45,7 @@ _signals = Namespace()
 # Core signals.  For usage examples grep the source code or consult
 # the API documentation in docs/api.rst as well as docs/signals.rst
 template_rendered = _signals.signal('template-rendered')
+before_render_template = _signals.signal('before-render-template')
 request_started = _signals.signal('request-started')
 request_finished = _signals.signal('request-finished')
 request_tearing_down = _signals.signal('request-tearing-down')

flask/templating.py

@@ -12,7 +12,7 @@ from jinja2 import BaseLoader, Environment as BaseEnvironment, \
      TemplateNotFound
 
 from .globals import _request_ctx_stack, _app_ctx_stack
-from .signals import template_rendered
+from .signals import template_rendered, before_render_template
 
 
 def _default_template_ctx_processor():
@@ -102,6 +102,7 @@ class DispatchingJinjaLoader(BaseLoader):
 
 def _render(template, context, app):
     """Renders the template and fires the signal"""
+    before_render_template.send(app, template=template, context=context)
     rv = template.render(context)
     template_rendered.send(app, template=template, context=context)
     return rv

tests/test_signals.py

@@ -46,6 +46,30 @@ def test_template_rendered():
     finally:
         flask.template_rendered.disconnect(record, app)
 
+def test_before_render_template():
+    app = flask.Flask(__name__)
+
+    @app.route('/')
+    def index():
+        return flask.render_template('simple_template.html', whiskey=42)
+
+    recorded = []
+
+    def record(sender, template, context):
+        context['whiskey'] = 43
+        recorded.append((template, context))
+
+    flask.before_render_template.connect(record, app)
+    try:
+        rv = app.test_client().get('/')
+        assert len(recorded) == 1
+        template, context = recorded[0]
+        assert template.name == 'simple_template.html'
+        assert context['whiskey'] == 43
+        assert rv.data == b'<h1>43</h1>'
+    finally:
+        flask.before_render_template.disconnect(record, app)
+
 def test_request_signals():
     app = flask.Flask(__name__)
     calls = []