Python class __init__(mandatory arguments?)

[Ray Smith]

Lee John Moore <leej at dsl.pipex.com> wrote in message news:<bcitu2$jrrv8$1 at ID-129053.news.dfncis.de>...
> Just for confirmation really: When I create a custom class, is
> it *really* true that def __init__() arguments can only ever be
> optional?  Eg:

No, not that I know of.  
 
> class MyClass:
> 	param1 = None
> 	param2 = None
> 	def __init__(self, param1, param2):
> 		param1 = self.param1
> 		param2 = self.param2
> 
> myinstance1 = MyClass()
> myinstance2 = MyClass("Hello", "World")

the case of:

myinstance1 = MyClass()

should fail as far as I know.

I think what you want is something like:

class MyClass:
   def __init__(self, param1=None, param2=None):
      self.param1 = param1
      self.param2 = param2

myinstance1 = MyClass()
myinstance2 = MyClass("Hello", "World")

Also note you had the use of self backwards in your __init__() method.

> 
> I'm really unhappy that myinstance1 is allowed.  ;-)

As I said I didn't think it was.
 
> I'm so accustomed to constructor arguments being mandatory in
> C++ & OP classes....and yes, yes, I realise __init__() is not a
> constructor (even though it looks like one), but if there's a
> way I can *force* arguments upon class instantiation, I'd like
> to know about it. :-)

Just try playing around in Python with what you have said and see 
what happens.

Regards,

Ray Smith