Loss of precision / data corruption with Tkinter.DoubleVar ?!

[Lonnie Princehouse]

Greetings, 

I stumbled across this curiosity yesterday:

>>> x = 0.33333333333333098
>>> x
0.33333333333333098     
>>> import Tkinter
>>> y = Tkinter.DoubleVar(Tkinter.Tk())
>>> y.set(x)
>>> y.get()
0.33333333333300003  

What the....?

Sure, it's only on the order of 10e-13 delta, 
but why is there any difference at all??


I hit this because at some point I was trying to do:

y.set(x)
.
.
.
if y.get() == x:
    ...

and of course it wasn't working properly!

I have tried this on Python 2.2 for Win32 and Linux/x86




-Lonnie Princehouse