import sys
import cairo, gi
gi.require_version('Gtk', '2.0')
gi.require_version('Gdk', '2.0')
gi.require_version('WebKit', '1.0')
from gi.repository import Gtk, Gdk, WebKit

if len(sys.argv) != 3:
    print 'usage: %s url filename'%sys.argv[0]
    sys.exit(-1)

uri, filename = sys.argv[1:]

for scheme in ('http://', 'https://', 'ftp://', 'file://'):
    if uri.startswith(scheme):
        break
else:
    uri = 'http://' + uri

w = Gtk.OffscreenWindow()
w.set_default_size(800, 640)
v = WebKit.WebView()
w.add(v)

def capture_window(window):
    w, h = window.get_size()
    dst = cairo.ImageSurface(cairo.FORMAT_ARGB32, w, h)
    ctx = cairo.Context(dst)
    surface = Gdk.cairo_create(window.get_window()).get_target()
    ctx.set_source_surface(surface)
    ctx.paint()
    dst.write_to_png(filename)
    Gtk.main_quit()

def progress_cb(webview, progress, window):
    if webview.get_progress() == 1.0:
        capture_window(window)

v.connect('notify::progress', progress_cb, w)
v.load_uri(uri)
w.show_all()

Gtk.main()