python 2.7 __init__ behavior on self

I have a python question that I'm sure is pretty simple - please feel free to disabuse me of any sort of bad practice while you're at it. I have the following code:

class User(dict,BaseDBI):
    def __init__(self,uid=None,username=None):
        self['uid']=str(uuid())     
        if uid == None and username is not None:            
            uid_struct = self.Get('data/username.kch',username)         
            if uid_struct is not None:
                self = self.Get('data/user.kch',uid_struct['uid'])

As you can tell this User is simply an extended dict object. It also accesses a few simple Get and Set methods on a couple of Kyoto Cabinet db files. I put in some print statements to trace through what's going on and everything is being set properly, but when I create a User object (e.g.):

user = User(username='someusername')

and then print user I only hav开发者_如何学JAVAe a new dict object that has the brand new uid generated by the first line under __init__

Thanks for any wisdom!

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python variables are references. when you assign to self, you are replacing that reference but not altering the object which is returned by __init__.

The easiest thing may be to simply use the dict.update method to copy all key/value pairs into self. This should 'just work' since you're already inheriting from dict.

Inheritance is only appropriate for a relationship like A is a B. You indicate that a User is a dict, that's fine, but I doubt that a User is a BaseDBI. It's more likely that you want a User to have a database, in which case composition is more appropriate. This probably seems nit-picky, but will prevent you from making bizarre and obscene systems.

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You need to call the inherited constructors. Something like:

def __init__(self,uid=None,username=None):
    dict.__init__(self)
    BaseDBI.__init__(self)

Also assigning to self will just replace the value in the local variable self. It will not have any effect on the object.

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If you need to return an already existing instance or your class, you need to define a __new__ method

By the time __init__ is called, a fresh instance has already been created