src/Census.py

   1 import pgdb
   2
   3 import GPS
   4
   5
   6 class Database:
   7     """
   8     This class wraps all of the operations that we'd like to perform
   9     on the census database. Most of the utility scripts will just call
  10     one or two methods from within this class.
  11     """
  12
  13     def __init__(self, _host, _database, _username, _srid):
  14         self.connection = pgdb.connect(host=_host,
  15                                        database=_database,
  16                                        user=_username)
  17         self.srid = _srid
  18
  19
  20     def __del__(self):
  21         self.connection.close()
  22
  23
  24     def find_average_population_density(self, coords):
  25         """
  26         Find the average population density at a set of GPS coordinates.
  27         """
  28         cursor = self.connection.cursor()
  29
  30         query = """
  31         SELECT population_density
  32         FROM (sf1_blocks INNER JOIN tiger
  33               ON sf1_blocks.tiger_blkidfp00=tiger.blkidfp00)
  34         WHERE ST_Contains(tiger.the_geom,
  35                           ST_SetSRID(ST_Point(%.6f, %.6f), %d));
  36         """
  37
  38         sql_params = (coords.longitude, coords.latitude, self.srid)
  39         cursor.execute(query, sql_params)
  40         rows = cursor.fetchall()
  41
  42         if len(rows) > 0:
  43             return rows[0][0]
  44         else:
  45             return None
  46