Mysterious "Attribute Errors" when GUI Programming

[Steve Holden]

Coral Snake wrote:
> I am having problems with programming even simple "Hello World"
> programs from books and tutorials that use Python GUI libraries. Such
> Programs cause python to throw "Attribute Errors" even when the
> "attributes" being asked for by the errors exist in the source code.
> This has happened to me in both the standard python GUI Library Tkinter
> and in pyGTK here are the codes for the "Hello World Programs involved
> and their corosponding "Attribute Errors":
> 
> ----------------------------------------------------------
> Tkinter:
> 
> from Tkinter import *
> root = Tk()
> win = Toplevel(root)
> win.pack()
> Label(win, text= "Hello, Python World").pack(side=TOP)
> Button(win, text= "Close", command=win.quit).pack(side=RIGHT)
> win.mainloop()
> ---------------------------------------------------------
> 
> AttributeError: Toplevel instance has no attribute 'pack'
> 
> ---------------------------------------------------------
> pyGTK
> 
> import pygtk
> pygtk.require('2.0')
> import gtk
> 
> class HelloWorld:
>    def hello(self, widget, data=None):
>       print "Hello World"
> 
>    def delete_event(self, widget, event, data= None):
>       print "delete event occured"
>       return gtk.FALSE
> 
>    def destroy(self, widget, data = None):
>       gtk.main_quit()
> 
>    def __init__(self):
>       self.window = gtk.Window(gtk.WINDOW_TOPLEVEL)
>       self.window.connect("delete_event", self.delete_event)
>       self.window.connect("destroy", self.destroy)
>       self.window.set_border_width(10)
>       self.button = gtk.Button("Hello, World!")
>       self.button.connect("clicked", self.hello, None)
>       self.button.connect_object("clicked",
>       gtk.Widget.destroy, self.window)
>       self.window.add(self.button)
>       self.button.show()
>       self.window.show()
> 
>       def main(self):
>          gtk.main()
> 
> if __name__ == "__main__":
>    hello = HelloWorld()
>    hello.main()
> 
> ------------------------------------------------------------
> 
> AttributeError: HelloWorld instance has no attribute 'main'
> 
> ------------------------------------------------------------
> As you can see if you look at this code the "attributes"
> being asked for by both programs exist in the source code but python
> insists that they DON'T. What I want to know is what kind of bugs
> either in my source code or in Python itself leads it to to throw these
> "Attribute Errors" when the "attribute" being asked for by the error
> exists in the source code.
> 

There's absolutely no point trying do divine how to write Tkinter-based 
programs by reading the source, though it's a brave approach. But ...

  >>> from Tkinter import *
  >>> root = Tk()
  >>> win = Toplevel(root)
  >>> "pack" in dir(win)
  False
  >>>

tells you, absolutely beyond a shadow of a doubt, that Toplevel windows 
don't have a "pack" method.

Take a look at a few of the working examples of Tkinter programs, that 
should tell you what you are doing wrong.

regards
  Steve