add formencode.Schema subclass for convenience

edbob/pyramid/forms/simpleform.py

@@ -26,15 +26,29 @@
 ``edbob.pyramid.forms.simpleform`` -- pyramid_simpleform Forms
 """
 
-import pyramid_simpleform
 from pyramid.renderers import render
+
+import formencode
+import pyramid_simpleform
 from pyramid_simpleform.renderers import FormRenderer
 
 from edbob.pyramid import helpers
 from edbob.pyramid.forms import Form
 
 
-__all__ = ['SimpleForm']
+__all__ = ['Schema', 'SimpleForm']
+
+
+class Schema(formencode.Schema):
+    """
+    Subclass of ``formencode.Schema``, which exists only to ignore extra
+    fields.  These normally would cause a schema instance to be deemed invalid,
+    and pretty much *every* form has a submit button which would be considered
+    an extra field.
+    """
+
+    allow_extra_fields = True
+    filter_extra_fields = True
 
 
 class SimpleForm(Form):