Setting Class Attributes

[Bruno Desthuilliers]

the.theorist a écrit :
> I have a small, simple class which contains a dictionary (and some
> other stuff, not shown). I then have a container class (Big) that holds
> some instances of the simple class. When I try to edit the elements of
> the dictionary, all instances obtain those changes; I want each
> instance to hold separate entries.
> 
> #----------Begin module test.py
> class ex:

class ex(object): # oldstyle classes are deprecated

>     def __init__(self, val={}):
>         self.value = val

You didn't search very long. This is one of the most (in)famous Python 
gotchas: default args are evaluated *only once*, when the function 
definition is evaluated (at load time). This is also a dirty trick to 
have a 'static' (as in C) like variable.

The solution is quite simple:
class ex(object):
   def __init__(self, val=None):
     if val is None: val = {}
     self.value = val

(snip)