How to maintain scroll-region view while changing canvas size?

[syed_saqib_ali at yahoo.com]

Please take a look at and run the code snippet shown below.

It creates a canvas with vertical & Horizontal scroll-bars.
If you shrink the window to smaller than the area of the canvas, the
scroll-bars work as advertised. That's great.

However, if you click the Left Mouse button, it calls code which
expands the width of the canvas by 100 pixels. The area being viewed
expands correspondingly..... BUT I DON'T WANT IT TO!!

I want to know how to expand the size of a canvas without changing the
area/size of what is currently shown by the scroll bars. I would like
to find code that expands the width of the canvas and simply adjusts
the H-Scrollbar without changing what is shown on in the area of the
canvas being displayed.

I have tried seemingly every combination of messing with the
canvas.config and scrollregion parameters to no avail. Can someone out
there show me how its done??

-Saqib






-----------------------------------------
import Tkinter

def _b1PressEvt(event):
    print "B1"
    _canvas.config(width=300)


tkRoot = Tkinter.Tk()
_canvas = Tkinter.Canvas(tkRoot, background="white", width=200,
height=200,)


# Scroll Bars
vScrollbar = Tkinter.Scrollbar(tkRoot)
vScrollbar.pack(side=Tkinter.RIGHT, expand=True, fill=Tkinter.Y)

hScrollbar = Tkinter.Scrollbar(tkRoot)
hScrollbar.pack(side=Tkinter.BOTTOM, expand=True, fill=Tkinter.X)


_canvas.config(
    width=200,
    height=200,
    scrollregion=(0,0,100,100),
    yscrollcommand=vScrollbar.set,
    xscrollcommand=hScrollbar.set,
)

vScrollbar.config(orient=Tkinter.VERTICAL, command=_canvas.yview)
hScrollbar.config(orient=Tkinter.HORIZONTAL, command=_canvas.xview)

#tkRoot.pack()
_canvas.pack(expand=Tkinter.NO)
vScrollbar.pack(side=Tkinter.RIGHT, expand=True, fill=Tkinter.Y)
hScrollbar.pack(side=Tkinter.BOTTOM, expand=True, fill=Tkinter.X)


# Function Bindings
_canvas.bind("<Button-1>", _b1PressEvt)


tkRoot.mainloop()