skualo.py

browser = browser()
browser.get("http://www.skualo.cl/ERP/login.aspx")

elem = browser.css("#txtIDUsuario")
elem.send_keys("")

elem = browser.css("#txtPassword")
elem.send_keys("")

elem = browser.css("#bttIngresar").click()
elem = browser.css("#bttContinuar").click()

url = "http://www.skualo.cl/ERP/FIN/RPT/rptResultadoMensual.aspx"
browser.get(url)

browser.css("#ctl00_contenido_cmbMes option[value='8']").click()
browser.css("#ctl00_contenido_cmbFormatoSalida option[value='XLS']").click()

data = [(x.get_attribute("name"), x.get_attribute("value")) for x in browser.css("form#aspnetForm select")]  + \
       [(x.get_attribute("name"), x.get_attribute("value")) for x in browser.css("form#aspnetForm input[type=hidden]")] + \
       [(x.get_attribute("name"), x.get_attribute("value")) for x in browser.css("form#aspnetForm input[type=submit]") if x.get_attribute("name") != 'ctl00$contenido$bttSalir'] + \
       [(x.get_attribute("name"), x.get_attribute("value")) for x in browser.css("form#aspnetForm input[type=checkbox]")]


headers = {'User-Agent' : 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:39.0) Gecko/20100101 Firefox/39.0'}

cookies = dict([(x['name'], x['value']) for x in browser.get_cookies()])

# Save file
with open('reporte.xls', 'wb') as f:
     r = requests.post(url, data=dict(data), cookies=cookies, headers=headers)
     f.write(r.content)

browser.close()