Create PNG from Shapefile - handle multiple parts

gistfile1.py

import shapefile
import pngcanvas

# Open shapefile with Python Shapefile Library
shapefile_name = 'REPLACE_WITH_SHAPEFILE_NAME' # e.g. england_oa_2001
r = shapefile.Reader(shapefile_name)

# Determine bounding box x and y distances and then calculate an xyratio
# that can be used to determine the size of the generated PNG file. A xyratio
# of greater than one means that PNG is to be a landscape type image whereas
# an xyratio of less than one means the PNG is to be a portrait type image.
xdist = r.bbox[2] - r.bbox[0]
ydist = r.bbox[3] - r.bbox[1]
xyratio = xdist/ydist
image_max_dimension = 1800 # Change this to desired max dimension of generated PNG
if (xyratio >= 1):
    iwidth  = image_max_dimension
    iheight = int(image_max_dimension/xyratio)
else:
    iwidth  = int(image_max_dimension*xyratio)
    iheight = image_max_dimension

# Iterate through all the shapes within the shapefile and draw polyline
# representations of them onto the PNGCanvas before saving the resultant canvas
# as a PNG file
xratio = iwidth/xdist
yratio = iheight/ydist
pixels = []
c = pngcanvas.PNGCanvas(iwidth,iheight)
for shape in r.shapes():
    for i, (x,y) in enumerate(shape.points):
        if i != 0 and i in shape.parts:
            c.polyline(pixels)
            pixels = []
        px = int(iwidth - ((r.bbox[2] - x) * xratio))
        py = int((r.bbox[3] - y) * yratio)
        pixels.append([px,py])
    c.polyline(pixels)
    pixels = []

with open('output.png', 'wb') as f:
    f.write(c.dump())