first commit

helix/forms/conditional_validator.py

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+from wtforms.validators import Optional
+
+
+class ConditionalValidator(object):
+    def __init__(self, other_field_name, other_data_contents, dependent_validator):
+        self.other_field_name = other_field_name
+        self.other_data_contents = other_data_contents
+        self.dependent_validator = dependent_validator
+
+    def __call__(self, form, field):
+        other_field = form._fields.get(self.other_field_name)
+        if other_field is None:
+            raise Exception('no field named "%s" in form' % self.other_field_name)
+        if other_field.data in self.other_data_contents:
+            self.dependent_validator.__call__(form, field)
+        else:
+            Optional().__call__(form, field)