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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def diff_write_only(resource):
 """A different implementation of diff that is used for those Vault resources that are write-only such as AWS root configs"""

        if resource.present and not resource.existing:
            return ADD
        elif not resource.present and resource.existing:
            return DEL
        elif resource.present and resource.existing:
            return OVERWRITE

        return NOOP