rounding errors?

[todd]

Hi, 
I've just started using Python, and am having an extraordinary experience.
One thing worries me, however,  I'm planning on doing some mathematical
research with Python, and it appears that it does funny thing with
floating point numbers..  Maybe It's superficial, but here's what I'm
getting,using the interpreter..
>>> .31
0.31
>>> .32
0.32000000000000001
>>> .33
0.33000000000000002
>>> .34
0.34000000000000002
>>> .35
0.34999999999999998
>>> .21
0.20999999999999999
>>> 
Now, I realize that this is really small errors.. Does anybody have an
explanation why Python picks up or loses these?
Thanks
Todd