graphic scale

Hi,

I am a new user of matplotlib.
I have already plot some data whit it but, I can't find the way to control the axis scales ...
I know how to define the min/max number for each axis. Is it possible to define the intermediate scale values ??
For example , the x - axis marks are (automatically) choosen :0 , 0.2 , 0.4 , 0.6 , 0.8 , 1.0
Can I have instead the values 0, 0.5 , 1.0 written on the axis ?

Best regards,
Xavier.