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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 list_scans(self, source_id=None):
 """ Filterable list of Scans for a Source. Ordered newest to oldest by default """

        if source_id:
            target_url = self.client.get_url('SCAN', 'GET', 'multi', {'source_id': source_id})
        else:
            target_url = self.client.get_ulr('SCAN', 'GET', 'all')
        return base.Query(self.client.get_manager(Scan), target_url)