Multiple constructors

[vincent wehren]

Philip Smith wrote:
> Call this a C++ programmers hang-up if you like.
> 
> I don't seem to be able to define multiple versions of __init__ in my matrix 
> class (ie to initialise either from a list of values or from 2 dimensions 
> (rows/columns)).
> 
> Even if Python couldn't resolve the __init__ to use on the basis of argument 
> types surely it could do so on the basis of argument numbers???
> 
> At any rate - any suggestions how I code this????

Checking the number of arguments ain't all that hard:

class Klass:
    def __init__(*args):
        self.args = args
        if len(self.args) == 1:
            # etc.

This feels rather unpythonic, though. Maybe you could use factory 
functions, forgetting about  __init__ all together (2.2 or higher):

class Klass(object):

     def fromList(seq):
         result = Klass()
         # populate attributes here
         # and return the requested object
         return result

     fromList = staticmethod(fromList)

     def fromDimensions(cols, rows):
         result = Klass()
         # populate attributes here
         # and return the requested object
         return result

    fromDimensions = staticmethod(fromDimensions)

    #more methods  here


k = Klass.fromList(seq)
etc..


Regards
--

Vincent Wehren







> 
> Thanks
> 
> Phil 
> 
>