Overloaded Constructors?!?

Michael Spencer mahs at telcopartners.com
Mon Mar 21 00:27:04 CET 2005


andrea_gavana at tin.it wrote:
>  [trying to create a single Python class with the equivalent of the following overloaded constructors]
> 
> wxFoldWindowItem(wxWindow *wnd, int flags = wxFPB_ALIGN_WIDTH,
>                  int ySpacing = wxFPB_DEFAULT_YSPACING,
>                  int leftSpacing = wxFPB_DEFAULT_LEFTSPACING, 
>                  int rightSpacing = wxFPB_DEFAULT_RIGHTSPACING)
> 
> or
> 
> wxFoldWindowItem(int y, const wxColour &lineColor = *wxBLACK, 
>                  int ySpacing = wxFPB_DEFAULT_YSPACING,
>                  int leftSpacing = wxFPB_DEFAULT_LEFTLINESPACING,
>                  int rightSpacing = wxFPB_DEFAULT_RIGHTLINESPACING)


Several options in addition to the factory function that Kent has suggested (and 
  I'll assume he'll follow up with clarification)

# Option 1: one abstract base class holding all/most of the methods, and two 
separate subclasses reflecting the two use-cases.

class _AbstractFoldWindowItem(object):
     def __init__(self, *args, **kw):
         raise NotImplemetedError

     def
     ... all the shared methods

then

class FoldWindowItem(_AbstractFoldWindowItem):
     def __init__(self, wxWindow, flags = wxFPB_ALIGN_WIDTH,
                  ySpacing = wxFPB_DEFAULT_YSPACING,
                  leftSpacing = wxFPB_DEFAULT_LEFTSPACING,
                  rightSpacing = wxFPB_DEFAULT_RIGHTSPACING):

class FoldSeparator(_AbstractFoldWindowItem):
     def __init__(self, y, lineColor = wx.BLACK,
                  ySpacing = wx.FPB_DEFAULT_YSPACING,
                  leftSpacing = wx.FPB_DEFAULT_LEFTLINESPACING,
                  rightSpacing = wx.FPB_DEFAULT_RIGHTLINESPACING):


# Option 2: One class, two constructors:

class FoldWindowItem():

     def __init__(self, wxWindow, flags = wxFPB_ALIGN_WIDTH,
                  ySpacing = wxFPB_DEFAULT_YSPACING,
                  leftSpacing = wxFPB_DEFAULT_LEFTSPACING,
                  rightSpacing = wxFPB_DEFAULT_RIGHTSPACING):
         """Initializes with wxWindow"""
         self._type = wx.Window

     @classmethod
     def FromSeparator(cls, y, lineColor = wx.BLACK,
                  ySpacing = wx.FPB_DEFAULT_YSPACING,
                  leftSpacing = wx.FPB_DEFAULT_LEFTLINESPACING,
                  rightSpacing = wx.FPB_DEFAULT_RIGHTLINESPACING):
         newobj = cls.__new__(y, lineColor = wx.BLACK,
                  ySpacing = wx.FPB_DEFAULT_YSPACING,
                  leftSpacing = wx.FPB_DEFAULT_LEFTLINESPACING,
                  rightSpacing = wx.FPB_DEFAULT_RIGHTLINESPACING)
         newobj._type = wx.SEPARATOR
         # other initializatio
         return newobj

This requires the user code to call the class in two ways depending on how it is 
to be used:

i.e., myFoldWindowItem = FoldWindowItem(Window)
or myFoldWindowItem = FoldWindowItem.FromSeparator(y)



# Option 3: inspect the arguments and provide the signature details in the docstring

class FoldWindowItem():

     def __init__(self, obj, **kw):
         """Initialize with:
                  wxWindow, flags = wxFPB_ALIGN_WIDTH,
                  ySpacing = wxFPB_DEFAULT_YSPACING,
                  leftSpacing = wxFPB_DEFAULT_LEFTSPACING,
                  rightSpacing = wxFPB_DEFAULT_RIGHTSPACING)

             or:
                  y, lineColor = wx.BLACK,
                  ySpacing = wx.FPB_DEFAULT_YSPACING,
                  leftSpacing = wx.FPB_DEFAULT_LEFTLINESPACING,
                  rightSpacing = wx.FPB_DEFAULT_RIGHTLINESPACING)"""

         if isinstance(obj, wx.Window):
             # Do one thing
         elif isinstance(obj, wx.SEPARATOR):
             # Do the other


HTH

Michael




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