[wxPython-users] A Question of Style

[Christopher Barker]

>>   The method, 'OnFileNew' is called thusly:
>>
>>   def menuData(self):
>>     return (('&File',
>>               ('&New \tCtrl-N', 'Create a new project',  self.OnFileNew),
>>                 ...
>>   I'm obviously referencing the method incorrectly, but I don't see my
>> error. A pointer would be very helpful.
> 
> I'm not sure without seeing all the code, but maybe you are trying to 
> implement it the way it could be done in C++, where the methods of a 
> class can be spread across several source files.  Can't be done in 
> Python;

That's not entirely true: you just can't call them quite the same way. 
For example, from the above:

def menuData(self):
      return (('&File',
               ('&New \tCtrl-N', 'Create a new project', self.OnFileNew),

"self.InfileNew" means that InFileNew is a member of this class (self). 
If you had written:

def menuData(self):
      return (('&File',
                ('&New \tCtrl-N',
                 'Create a new project',
                 MethodsModule.OnFileNew),

it way have worked.

However, the main point is true -- you generally don't want to do that, 
methods belong in the class that they are used in -- that's why they are 
called methods, rather than functions. In the above, I suspect that 
OnfileNew belongs in the Frame subclass you're writing -- that's where 
menu handlers usually go.

It's still not totally clear why you are trying to re-factor in this 
way, but I suspect it's to follow the DRY (Don't Repeat Yourself) 
principle. This is a good instinct. If you find yourself writing the 
same code in more than one place -- it's time for a refactor.

What I'm guessing is that you have a few classes that all share similar 
methods, so you tried to put those in their own file. That can be done 
but it's not the OO way to do it. The OO way is subclassing. If you have 
a bunch of notebook pages, they should probably all be derived from the 
same class -- the methods common to all of them go there, and that 
superclass can be defined in it's own module, if you like.

If things get more complicated, it could be time for multiple 
inheritance and mix-ins. If you google mix-ins, you'll probably get lots 
of stuff, but here's quick explanation:

There are times when you have a bunch of classes which share some of the 
same functionality, but not all. I finally got this when I tried to 
apply DRY to wx.lib.floatcanvas, so I'll use that as an example:

All the objects you might want to draw on the screen are derived from 
DrawObject. This class holds common functionality for all kinds of 
shapes. However, I found that there are multiple types of objects, all 
with overlapping functionality: For instance, some have only a line 
(lines, polylines), some have both a line and a fill ( circles, 
polygons, rectangles). Some have their position defined in terms of a 
single (X,Y) point (circles, text), some by a set of points (Polygons, 
polylines). To accommodate this, I set up a bunch of mixins - classes 
that don't do anything by themselves, but provide methods that are comon 
to more than one, but not all of the DrawObjects:

PointsObjectMixin
LineOnlyMixin
LineAndFillMixin

etc, etc.

Now to make a new kind of DrawObject, you can jsut piece together the 
functionality required, and most of the work is done with the mixins. 
For example, the Line class has just two of its own methods:

class Line(DrawObject,PointsObjectMixin,LineOnlyMixin):
     def __init__(self,Points,
                  LineColor = "Black",
                  LineStyle = "Solid",
                  LineWidth    = 1,
                  InForeground = False):
         DrawObject.__init__(self, InForeground)

         ...
         ...


     def _Draw(self, dc , WorldToPixel, ScaleWorldToPixel, HTdc=None):
	
         ...
         ...


- I hope that helps,

-Chris










-- 
Christopher Barker, Ph.D.
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