Replace tokens in a mapnik sql query with values for a specified tile

test-mapnik-sql.py

#!/usr/bin/env python3

import logging
from optparse import OptionParser
import os
import sys
import mercantile

def _main():
    usage = "usage: %prog"
    parser = OptionParser(usage=usage,
                          description="")
    parser.add_option("-d", "--debug", action="store_true", dest="debug",
                      help="Turn on debug logging")
    parser.add_option("-q", "--quiet", action="store_true", dest="quiet",
                      help="turn off all logging")
    parser.add_option("-t", "--tile", dest="tile", default="14/2599/6317")

    (options, args) = parser.parse_args()
 
    logging.basicConfig(level=logging.DEBUG if options.debug else
    (logging.ERROR if options.quiet else logging.INFO))

    tile_tokens = options.tile.split("/")
    if len(tile_tokens) != 3:
        logging.error("invalid tile, must be in z/x/y format")
        sys.exit(-1)

    z, x, y = [int(f) for f in tile_tokens]
    logging.debug("Using tile %d/%d/%d" % (z, x, y))

    if z < 0 or z > 22:
        logging.error("Error, invalid zoom")
        sys.exit(-1)

    tile_bounds = mercantile.xy_bounds(x, y, z)

    if len(args) == 0 or args[0] == "-":
        sql_query = "".join(sys.stdin.readlines())
    else:
        with open(args[0], "r") as f:
            sql_query = str(f.read())

    pixel_width = 156412
    scale_denominator = 559082264.028
    for i in range(z):
        scale_denominator = scale_denominator / 2.0
        pixel_width = pixel_width / 2.0

    sql_query = sql_query.replace("!bbox!", 
        "ST_SetSRID('BOX3D(%f %f,%f %f)'::box3d,900913)" % 
        (tile_bounds.left, tile_bounds.bottom, tile_bounds.right, tile_bounds.top))
    sql_query = sql_query.replace("!scale_denominator!", str(scale_denominator))
    sql_query = sql_query.replace("!pixel_width!", str(pixel_width))
    sql_query = sql_query.replace("!pixel_height!", str(pixel_width))

    print(sql_query)

if __name__ == "__main__":
    _main()