しちゃだめ

# -*- coding: utf-8 -*-

class Obj:
    string = u''
    prop = u''

def printItem(lst):
    print u'items:'
    for item in lst:
        print item.string
        print item.prop

a = Obj()
a.string = u'A'
a.prop = u'null'

b = Obj()
b.string = u'B'
b.prop = u'null'

c = Obj()
c.string = u'C'
c.prop = u'null'

lst = [a, b, c]

printItem(lst)

for item in lst:
    if item.string == u'B':
        lst.remove(item)
        continue
    else:
        item.prop = u'_add'

printItem(lst)

items:
A
null
B
null
C
null
items:
A
_add
C
null