Bug?? reusing objects

[Peter Hansen]

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

[snip example using default parameter]
> -------------------------------------------------------------
> If this is expected behavior, could someone please explain it?
> Otherwise, I'll be happy to file a bug report.

Not a bug.  Default parameters are evaluated once at function
definition time, and used repeatedly thereafter.  There is
only one empty list there, no matter how many times you create
a new object.  Works for simple functions too:

>>> def fun(test=[]):
...   test.append('x')
...   print test
...
>>> fun()
['x']
>>> fun()
['x', 'x']

I believe this is a FAQ...

-Peter