GAE - Handing Custom Error Page

Java

<static-error-handlers>
  <handlerfile="default_error.html" />
  <handlerfile="over_quota.html"error-code="over_quota" />
</static-error-handlers>

Python

error_handlers:
 -file:default_error.html
 -error_code:over_quota
  file:over_quota.html