[Tutor] passing arguments to a make a graph

[Alan Gauld]

"Che M" <pine508 at hotmail.com> wrote
> Thank you, Alan.   I started by adding a method called addPoints() 
> to my
> class as you recommend.  But now I don't know how to pass a list of 
> points
> to the addPoints() method.

You need to create an instance of a PlotPanel.

> class PlotPanel(wx.lib.plot.PlotCanvas):
>    def __init__(self, points=[], *args, **kwargs):
>    def addPoints(self, points):
>    def _drawGraph(self):

> #this button tells it to make a graph using "mypoints".
>
> def OnGraphButton(self, event):
>    mypoints = [(3,4), (5,6)]   #these to be used
>    PlotPanel.addPoints(PlotPanel,mypoints)

Instead of using the class create an instance(aka object)

       self.plotPanel = PlotPanel(mypoints,self.notebook1)

That creates an instance passing the mypoints list in
to youir init method along with the notebook1 that you
pass when you create an instance later(see below).

>    self.notebook1.AddPage(imageId=-1, 
> page=PlotPanel(self.notebook1),
>                                          select=True, 
> text='Weight')

This should use the plotPanel instance:

     self.notebook1.AddPage(imageId=-1, page=self.plotPanel,
                                          select=True,  text='Weight')

> The error I get using it this way is:
>
> TypeError:  unbound method addPoints() must be called with PlotPanel
> instance as first argument (got type instance instead)

Yep, You gotta have an instance to call the methods.
See my OOP topic for more on classes, objects etc.

> I'm lost.  Also, what does "self.points += points" mean?  What is 
> the +=
> operator?

x += 5

is shorthand for

x = x + 5

The same applies to -/* etc.
See my raw Materials topic for more info on operators.

HTH,


-- 
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld