[patch] data and error_dict should have defaults in django.forms.FormWrapper

Patch for ticket #2899

There's a problem with the patch, John: in Python, default values for parameters are evaluated when the function is created, not when it is executed. Your patch will result in all FormWrappers? sharing the same default dictionaries. You should change it to something like:

def __init__(self, manipulator, data=None, error_dict=None, edit_inline=True): 
    self.manipulator, self.data = manipulator, (data or {})
    self.error_dict = error_dict or {}

New version of [patch] with changes suggested by adurdin

The a or b thingy in Python is not good for default arguments. If you supply an empty dictionary as argument, it will be replaced silently with another object by the arg or {} expression. The failsafe approach is to manually test for None:

def f (arg=None):
    if arg is None:
        arg = {}

(In [4029]) Fixed #2899: added defaults for data and error_dict params to FormWrapper?. Thanks, john@sneeu.com.