code: def create(self, name, instance_dir=None, config='solrconfig.xml', schema='schema.xml'):
          
          params = {
              'action': 'CREATE',
              'name': name,
              'config': config,
              'schema': schema,
          }
  
          if instance_dir is None:
              params.update(instanceDir=name)
          else:
              params.update(instanceDir=instance_dir)
  
          return self._get_url(self.url, params=params)
docs: http://wiki.apache.org/solr/CoreAdmin#head-7ca1b98a9df8b8ca0dcfbfc49940ed5ac98c4a08