Re: Overloaded Constructors?!?
[EMAIL PROTECTED] wrote:
Hello NG,
I am trying to port a useful class from wxWidgets (C++) to a pure
Python/wxPython
implementation. In the C++ source code, a unique class is initialized with
2 different methods (???). This is what it seems to me. I have this
declarations:
class wxFoldWindowItem
{
// wxWindow constructor. This initialises the class as a wxWindow type
wxFoldWindowItem(wxWindow *wnd, int flags = wxFPB_ALIGN_WIDTH, int ySpacing
= wxFPB_DEFAULT_YSPACING,
int leftSpacing = wxFPB_DEFAULT_LEFTSPACING, int
rightSpacing
= wxFPB_DEFAULT_RIGHTSPACING)
: _wnd(wnd)
, _type(WINDOW)
, _flags(flags)
, _leftSpacing(leftSpacing)
, _rightSpacing(rightSpacing)
, _ySpacing(ySpacing)
, _lineWidth(0)
, _lineY(0)
{
};
// separator constructor. This initialises the class as a separator
type
wxFoldWindowItem(int y, const wxColour lineColor = *wxBLACK, int ySpacing
= wxFPB_DEFAULT_YSPACING,
int leftSpacing = wxFPB_DEFAULT_LEFTLINESPACING,
int rightSpacing = wxFPB_DEFAULT_RIGHTLINESPACING)
: _wnd(0)
, _type(SEPARATOR)
, _flags(wxFPB_ALIGN_WIDTH)
, _leftSpacing(leftSpacing)
, _rightSpacing(rightSpacing)
, _ySpacing(ySpacing)
, _lineWidth(0)
, _lineY(y)
, _sepLineColour(lineColor)
{
};
The 2 different initializations refers to completely different objects (the
first one is a wx.Window, the second one is an horizontal line).
This is a strange design. My first reaction is, why do you want to do that? Maybe you should split
the class in two?
Next, there
are a lot of functions that, depending on the variable _type, return properties
of the wx.Window or of the line. I would like to keep the same names for
classes/methods, so it would be useful to have the same class with 2 different
initializations.
One way to do this in Python is to have a single constructor that looks at the type / number of
arguments to figure out what it is supposed to do. Another way is to make two factory methods that
create instances of the class and do the correct initialization.
Kent
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Re: Overloaded Constructors?!?
[EMAIL PROTECTED] 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 -- http://mail.python.org/mailman/listinfo/python-list
Re: Overloaded Constructors?!?
[EMAIL PROTECTED] wrote:
Hello NG,
I am trying to port a useful class from wxWidgets (C++) to a pure
Python/wxPython
implementation. In the C++ source code, a unique class is initialized with
2 different methods (???). This is what it seems to me. I have this
declarations:
C++ code snipped
The 2 different initializations refers to completely different objects (the
first one is a wx.Window, the second one is an horizontal line).
Does anyone know if is there a way to achieve the same thing in Python/wxPython?
Someone else has talked about overloaded constructors, but I don't have
any idea on how to implement this kind of constructors in Python. Does
anyone have a small example of overloaded constructors in Python?
I have no idea... Or am I missing something obvious?
If you do have to do something like this you could use keyword arguments
with defaults. For example:
class C(object):
def __init__(self, a=None, b=None):
if None not in (a, b):
raise some error (only one of a/b should be given)
if a:
# do something
elif b:
# do something else
Another way to do it is to use classmethods:
class C(object):
def __init__(self):
# do initialization
def create_one(cls, a):
obj = cls()
# do something with a
return obj
create_one = classmethod(create_one)
def create_two(cls, b):
obj = cls()
# do something with b
return obj
create_two = classmethod(create_two)
Then you can use it thus:
x = C.create_one(a='value')
y = C.create_two(b='value')
Because it is a classmethod, calling C.create_one('value') calls
create_one() with two parameters:
- C
- 'value'
i.e. the first parameter is the class, not an instance of the class.
Hope this helped.
Shalabh
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Re: Overloaded Constructors?!?
Another way is to make two factory methods that create instances of the class and do the correct initialization. I am sorry to be so tedious, but I am still quite a newbie in Python... could you please provide a very small example of your last sentence? Looks quite interesting... See the recipe at this link. It defines a basic constructor to create Color objects using 3 integer args for red/green/blue, and a separate staticmethod as a factory method to create a Color using a single integer representing an RBG value. http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/223611 -- Paul (This recipe was taken from a much larger sample for basic bitmap drawing, which you will find at http://www.geocities.com/ptmcg/python/index.html#bmp .) -- http://mail.python.org/mailman/listinfo/python-list
