pbl.py

import gi
gi.require_version('GdkPixbuf', '2.0')
from gi.repository import GdkPixbuf
from urllib import request
import sys

pbl = GdkPixbuf.PixbufLoader()
url = sys.argv[1]

def prepped(*args):
    pb: GdkPixbuf.Pixbuf = pbl.get_pixbuf()
    print('prepped', pb, pb.get_width(), 'x', pb.get_height())

def updated(*args):
    print('updated', *args)

pbl.connect('area-prepared', prepped)
pbl.connect('area-updated', updated)

with request.urlopen(url) as fp:
    while True:
        buf = fp.read(1024)
        if not buf:
            break
        pbl.write(buf)
    pbl.close()

pb = pbl.get_pixbuf()
print('pixbuf', pb, pb.get_width(), 'x', pb.get_height())