Question on default value of __init__
bernie at pacific.net.hk
Mon Nov 19 11:42:29 CET 2001
Thanks for the confirmation, Werner. I am intented to use the null object
pattern, that is the reason why I use foo() as default.
Werner Schiendl wrote:
> yes, this is the default behaviour of Python.
> The default value you provide is stored and passed to every invokation of
> the function/method.
> This means, the _same_ instance of foo will be passed for every call to
> To get what you probably want, use None as the default and handle that
> special case by creating a new instance explicitely.
> This also prevents an instance of foo being created, before you create bar.
> "Bernie" <bernie at pacific.net.hk> wrote in message
> news:3BF8D3BC.105F0536 at pacific.net.hk...
> > Hello all,
> > When I run test.py, an instance of foo is created. Is this the default
> > in Python for default value? i.e. The value must be exist as an object.
> > there any way to delay the creation of foo() until bar() is created.
> > Bernie
> > test.py:
> > class foo:
> > def __init__( self, param=None):
> > print 'executed!'
> > self.__param = param
> > def __nonzero( self):
> > if self.__param:
> > return 1
> > else:
> > return 0
> > class bar:
> > def __init__( self, param=foo()):
> > assert isinstance( param, foo), '"in" must be an instance of
> > pass
More information about the Python-list