[Tutor] line class

[Paul McGuire]

> 
> > def __init__(self,p1,p2):
> >   self.p1 = p1
> >   self.p2 = p2
> >
> > And since a line should not have zero length (although you might argue 
> > with that!) you could also check if
> > p1==p2
> 
> In this case he should define Point.__cmp__() so the comparison is by
value rather than identity.
> 
> Kent
> 

I'd also suggest that in defining __cmp__ that the OP's test for equality
should comprehend some kind of epsilon value, if the x-y coordinates are
going to be floating point numbers.  It is very easy in graphical apps to
get tripped up by floating point round-off.  Here is a contrived but simple
demonstration:

>>> x = 1
>>> for i in range(10): x -= 0.1
...
>>> x
1.3877787807814457e-016
>>> x == 0
False

So instead of "if p1.x == p2.x" you should use "if abs(p1.x-p2.x) <
EPSILON", and define EPSILON to something in the range of 1e-13 or so.

-- Paul