Bug?? reusing objects

[Hans Nowak]

Damian Menscher wrote:
> 
> The following test program demonstrates what I believe is a bug:
> -------------------------------------------------------------
> #!/tmp/Python-2.2.1/python
> 
> class foobar:
>    def __init__(self, string=[]):
>       self.data = string
>    def add(self, new=""):
>       self.data.append(new)
> 
> a = foobar("foo")
> print a.data
> 
> a = foobar("bar")
> print a.data
> 
> a = foobar()
> print a.data
> 
> a.add("foo")
> a.add("bar")
> print a.data
> 
> a = foobar()
> print a.data   ### returns ['foo', 'bar'] for me
>                ### I'd expect it to return []
> -------------------------------------------------------------
> If this is expected behavior, could someone please explain it?
> Otherwise, I'll be happy to file a bug report.

It's a FAQ:

  http://www.python.org/cgi-bin/faqw.py?req=show&file=faq06.025.htp

"It is often expected that a function CALL creates new objects 
for default values. This is not what happens. Default values 
are created when the function is DEFINED, that is, there is 
only one such object that all functions refer to. If that 
object is changed, subsequent calls to the function will refer 
to this changed object. By definition, immutable objects 
(like numbers, strings, tuples, None) are safe from change. 
Changes to mutable objects (like dictionaries, lists, class 
instances) is what causes the confusion."

-- 
Hans (base64.decodestring('d3VybXlAZWFydGhsaW5rLm5ldA==')) 
# decode for email address ;-)
The Pythonic Quarter:: http://www.awaretek.com/nowak/