clases_como_funciones.py

from urllib.request import urlopen

class PlantillaUrl:
    def __init__(self, plantilla):
        self.plantilla = plantilla

    def abrir(self, **kwargs):
        return urlopen(self.plantilla.format_map(kwargs))


yahoo = PlantillaUrl('https://samples.openweathermap.org/data/2.5/forecast?id={id}&appid=b1b15e88fa797225412429c1c50c122a1')
for linea in yahoo.abrir(id='524901', appid='b1b15e88fa797225412429c1c50c122a1'):
    print(linea.decode('utf-8'))