I have this code :

def on_btn_login_clicked(self, widget):email = self.log_email.get_text()passw = self.log_pass.get_text()self.lbl_status.set_text("Connecting ...")params = urllib.urlencode({'@log_email': email, '@log_pass': passw, '@action': 'login', '@module': 'user'})headers = {"Content-type": "application/x-www-form-urlencoded","Accept": "text/plain"}conn = httplib.HTTPConnection("website.com")self.lbl_status.set_text("Logging in ...")conn.request("POST", "/ajax.php", params, headers)response = conn.getresponse()print response.statusself.lbl_status.set_text("")data = response.read()      print dataconn.close()

The self.lbl_status doesn't change till the request is finished, so it displays nothing due to the last set_text function.

Why is this happening, and how to avoid/fix that?

Below is a working example of a simple downloader for illustration purposes only. You need to use multi-threading if you want your GUI to be responsive and not freeze while you do some long running or blocking operation. I put this example together based on this stack overflow question and this excellent article Using threads in PyGTK. The default url an Ubuntu iso will take a while to download and should provide a good demonstration . You can enter any url you want when prompted it will download and save the file in the current directory.

from threading import Thread
import time
import gtk, gobject, urllibURL = 'http://releases.ubuntu.com//precise/ubuntu-12.04.1-desktop-i386.iso'def download(url):filename = url.split('/')[-1]out = open(filename, 'wb')gobject.idle_add(label.set_text, "connecting...")f = urllib.urlopen(url)buffer = f.read(1024)counter = 0while buffer:counter += len(buffer)out.write(buffer)msg = "downloaded {0:,} bytes".format(counter)gobject.idle_add(label.set_text, msg)buffer = f.read(1024)out.close()gobject.idle_add(label.set_text, "download complete")def clicked(button):url = entry.get_text()Thread(target=download, args=(url,)).start()gtk.gdk.threads_init()
win = gtk.Window()
win.set_default_size(400, 100)
entry = gtk.Entry()
entry.set_text(URL)
label = gtk.Label("Press the button")
button = gtk.Button(label="Download")
button.connect('clicked', clicked)box = gtk.VBox()
box.pack_start(entry)
box.pack_start(label)
box.pack_start(button)
win.add(box)win.show_all()gtk.main()