wxPython fetch remote image and threading

Question

I am trying to write an application in wxPython to display a few items from the Amazon store (for now only book covers as JPGs). I am using urllib2 and displaying them on a bitmap button and listing them for further action, but after coding it, the main window/app only seems to load after all the urls/images have been fetched..upon googling I understand that we must use Threads to break the operation while the apps main code runs, but this is my first attempt with wxpython and all the examples I have read confuse me even more.

I have mentioned below the code I am working with for any experts who can give me ideas on how to ensure each URL is fetched and displayed as it reads them... the code below is a amalgamation of various examples found here and the web so pls excuse my lack of skills..

import wx
import os
import sys
import urllib2
import cStringIO

urls = ['https://images-na.ssl-images-amazon.com/images/I/51-u3J3mtTL._AC_US100_.jpg',
        'https://images-na.ssl-images-amazon.com/images/I/51cRqX8DTgL._AC_US100_.jpg',
        'https://images-na.ssl-images-amazon.com/images/I/515iBchIIzL._AC_US100_.jpg',
        'https://images-na.ssl-images-amazon.com/images/I/511MaP7GeJL._AC_US100_.jpg',
        'https://images-na.ssl-images-amazon.com/images/I/51jizRmRYYL._AC_US160_.jpg']

class Example(wx.Frame):

    def __init__(self, *args, **kwargs):
        super(Example, self).__init__(*args, **kwargs) 
        self.InitUI()
        self.Ctrls()
        self.makeButtons()

    def makeButtons(self):

        i = 0

        for url in urls:

            f = urllib2.urlopen(url)
            data = f.read()

            i += 1
            print " url = ",url, "  ",i
            stream = cStringIO.StringIO(data)
            bmp = wx.BitmapFromImage( wx.ImageFromStream( stream ) )
            button = wx.Button(self.panel, -1, "Book cover", style=wx.ALIGN_CENTER, size=wx.Size(100,100))
            button.SetToolTipString("wx.Button can how have an icon on the left, right,\n"
                           "above or below the label.")
            button.SetBitmap(bmp,
                    wx.LEFT    # Left is the default, the image can be on the other sides too
                    #wx.RIGHT
                    #wx.TOP
                    #wx.BOTTOM
                    )
            button.SetBitmapMargins((4,4)) 
            button.SetFont(wx.Font(8, wx.SWISS, wx.NORMAL, wx.BOLD, False))
            self.wrapSizer.Add(button, 1, wx.EXPAND)
        self.Show(True)
        self.panel.Layout()

    def InitUI(self):
        self.SetSize((800, 400))
        self.SetTitle('Dynamically Flow Buttons to Next Row on Window-Resize')
        self.Centre()


    def Sizers(self):
        self.wrapSizer = wx.WrapSizer()
        self.panel.SetSizer(self.wrapSizer)

    def Ctrls(self):
        self.panel = wx.Panel(parent=self,pos=wx.Point(0,0), size=wx.Size(750,550), style=wx.TAB_TRAVERSAL)
        self.Sizers()

def main():

    ex = wx.App()
    Example(None)
    ex.MainLoop()

if __name__ == '__main__':
    main()

Answer 1

You should use threads for the url fetching and then use wx.CallAfter to return to the main thread to display the data... here is how your code can be changed

import threading

def makeButtons(self):


    def _update_data(data):

        stream = cStringIO.StringIO(data)
        bmp = wx.BitmapFromImage( wx.ImageFromStream( stream ) )
        button = wx.Button(self.panel, -1, "Book cover", style=wx.ALIGN_CENTER, size=wx.Size(100,100))
        button.SetToolTipString("wx.Button can how have an icon on the left, right,\n"
                       "above or below the label.")
        button.SetBitmap(bmp,
                wx.LEFT    # Left is the default, the image can be on the other sides too
                #wx.RIGHT
                #wx.TOP
                #wx.BOTTOM
                )
        button.SetBitmapMargins((4,4)) 
        button.SetFont(wx.Font(8, wx.SWISS, wx.NORMAL, wx.BOLD, False))
        self.wrapSizer.Add(button, 1, wx.EXPAND)
        self.Show(True)
        self.panel.Layout()

    def f():
        f = urllib2.urlopen(url)
        data = f.read()
        wx.CallAfter(_update_data, data)

    for url in urls:
        threading.Thread(target=f).start()