default value in __init__

[kenneth]

Dear all,

I have encountered this weird problem.

I have a class definition with an __init__ argument 'd'
which defaults to {}. This argument is put in the 'self.d'
attribute at initialization

I create two independent instances of this class; the code
is as follows.

class C:
  def __init__(self, i=10, d = {}):
    self.d = d
    self.i = i
  def get(self):
    print
    print self.d
  def set(self, dval, ival):
    self.d.update(dval)
    self.i+=ival

c1=C()
c1.set({'one':1},3)
c1.get()

del c1

c2=C()
c2.set({'two':2},4)
c2.get()


If I run the code I obtain:

{'one': 1}

{'two': 2, 'one': 1}

It seems that the 'self.d' argument of the second instance is the
same of the 'self.d' of the first (deleted!) instance.

Running the code in a debugger I discovered that, when I enter the
__init__ at the second initialization, before doing

self.d = d

the 'd' variable already contains the 'self.d' value of the first
instance and not the default argument {}.

Am I doing some stupid error, or this is a problem ?

Thanks in advance for any help,
Paolo