bin/find_avg_population_density

   1 #!/usr/bin/python
   2
   3 """
   4 Find the average population density of a set of GPS coordinates.
   5 """
   6
   7 import sys
   8 import os
   9 import site
  10
  11 # Basically, add '../src' to our path.
  12 # Needed for the imports that follow.
  13 site.addsitedir(os.path.dirname(os.path.abspath(sys.argv[0])) + '/../src')
  14
  15 import Census
  16 import CLI
  17 import Configuration.Defaults
  18 import ExitCodes
  19 import GPS
  20 import StringUtils
  21
  22
  23 """
  24 Parse the command line options. There's some magic involved here;
  25 otherwise, optparse woule like nothing more than to interpret GPS
  26 coordinates such as '-78.000000' as options.
  27 """
  28 for idx, value in enumerate(sys.argv):
  29     # Please oh please don't rename this script to something which
  30     # validates as a negative float.
  31     if (StringUtils.is_negative_float(value)):
  32         sys.argv.insert(idx, '--')
  33         # We have to break here, otherwise the negative argument
  34         # will get shifted down the list, and we'll hit it again
  35         # in the next iteration of enumerate(). And then it'll
  36         # get shifted down the list...
  37         break
  38
  39 usage = '%prog [options] <longitude> <latitude>'
  40
  41 parser = CLI.default_option_parser(usage)
  42
  43 # Use this module's docstring as the description.
  44 parser.description = __doc__
  45
  46 parser.add_option('-s',
  47                   '--srid',
  48                   type="int",
  49                   help="SRID of the input geometry. Defaults to %s." % Configuration.Defaults.SRID,
  50                   default=Configuration.Defaults.SRID)
  51
  52 (options, args) = parser.parse_args()
  53
  54 if len(args) < 2:
  55     print "\nERROR: You must supply a longitude and latitude.\n"
  56     parser.print_help()
  57     print '' # Print a newline
  58     raise SystemExit(ExitCodes.NOT_ENOUGH_ARGS)
  59
  60
  61 coords = GPS.Coordinates()
  62 coords.longitude = float(args[0])
  63 coords.latitude = float(args[1])
  64
  65 cdb = Census.Database(options.host,
  66                       options.database,
  67                       options.username,
  68                       options.srid)
  69
  70 avg_density = cdb.find_average_population_density(coords)
  71
  72 if (avg_density != None):
  73     print str(avg_density)
  74 else:
  75     print 'Error: No rows returned.'
  76     print 'Did you pass (longitude, latitude) in the correct order?'
  77     raise SystemExit(ExitCodes.NO_RESULTS)
  78