<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_public_dsn(self, scheme=None):
 """ Returns a public DSN which is consumable by raven-js """

        if self.is_enabled():
            url = self.remote.get_public_dsn()
            if scheme:
                return '%s:%s' % (scheme, url)

            return url