plotting arrow in python

[Gregory Ewing]

> rudra wrote:
> 
>> 0.0 0.0 0.1
>> 0.0 0.1 0.1
>> 0.1 0.0 0.5
>>
>> like that! the first two column are coordinate and 3rd one is
>> magnitude of moment (say: x y,m)!! so what i want to do is draw an
>> arrow of magnitude(m) in the position (x,y).

There seems to be some information missing there.
How do you know what direction to draw the arrow in?

-- 
Greg