create a base RESTError exception

moto/core/exceptions.py

@@ -0,0 +1,28 @@
+from werkzeug.exceptions import HTTPException
+from jinja2 import DictLoader, Environment
+
+
+ERROR_RESPONSE = u"""<?xml version="1.0" encoding="UTF-8"?>
+  <Response>
+    <Errors>
+      <Error>
+        <Code>{{code}}</Code>
+        <Message>{{message}}</Message>
+        {% block extra %}{% endblock %}
+      </Error>
+    </Errors>
+  <RequestID>7a62c49f-347e-4fc4-9331-6e8eEXAMPLE</RequestID>
+</Response>
+"""
+
+
+class RESTError(HTTPException):
+    templates = {
+        'error': ERROR_RESPONSE
+    }
+
+    def __init__(self, code, message, template='error', **kwargs):
+        super(RESTError, self).__init__()
+        env = Environment(loader=DictLoader(self.templates))
+        self.description = env.get_template(template).render(
+            code=code, message=message, **kwargs)

moto/ec2/exceptions.py

@@ -1,13 +1,9 @@
 from __future__ import unicode_literals
-from werkzeug.exceptions import BadRequest
-from jinja2 import Template
+from moto.core.exceptions import RESTError
 
 
-class EC2ClientError(BadRequest):
-    def __init__(self, code, message):
-        super(EC2ClientError, self).__init__()
-        self.description = ERROR_RESPONSE_TEMPLATE.render(
-            code=code, message=message)
+class EC2ClientError(RESTError):
+    code = 400
 
 
 class DependencyViolationError(EC2ClientError):
@@ -306,17 +302,3 @@ class InvalidCIDRSubnetError(EC2ClientError):
             "InvalidParameterValue",
             "invalid CIDR subnet specification: {0}"
             .format(cidr))
-
-
-ERROR_RESPONSE = u"""<?xml version="1.0" encoding="UTF-8"?>
-  <Response>
-    <Errors>
-      <Error>
-        <Code>{{code}}</Code>
-        <Message>{{message}}</Message>
-      </Error>
-    </Errors>
-  <RequestID>7a62c49f-347e-4fc4-9331-6e8eEXAMPLE</RequestID>
-</Response>
-"""
-ERROR_RESPONSE_TEMPLATE = Template(ERROR_RESPONSE)