我正在尝试实现 O'Reilly 的 Python Cookbook（第 2 版）中的一个食谱，但该食谱的一小部分无法正常工作。我希望有人能帮我找出原因。
配方是“5.14：使用评分功能增强字典类型”。我的大部分代码都可以正常工作，但是在尝试更改键的“排名”时出现错误。我在所有评论中都保留了作者的身份，因此任何试图提供帮助的人都会对“unders”和“dunders”的用途有一个很好的了解。尤其是“_rating”方面，我认为这会以某种方式导致错误。
错误：
File "rating.py", line 119, in <module>
r["john"]=20
File "rating.py", line 40, in __setitem__
del self._rating[self.rating(k)] ##
AttributeError: 'Ratings' object has no attribute 'rating'
代码：
class Ratings(UserDict.DictMixin, dict):
'''The implementation carefully mixes inheritance and delegation
to achieve reasonable performance while minimizing boilerplate,
and, of course, to ensure semantic correctness as above. All
mappings' methods not implemented below get inherited, mostly
from DictMixin, but, crucially!, __getitem__ from dict. '''
def __init__(self, *args, **kwds):
''' This class gets instantiated just like 'dict' '''
dict.__init__(self, *args, **kwds)
# self._rating is the crucial auxiliary data structure: a list
# of all (value, key) pairs, kept in "natural"ly-sorted order
self._rating = [ (v, k) for k, v in dict.iteritems(self) ]
self._rating.sort()
def copy(self):
''' Provide an identical but independent copy '''
return Ratings(self)
def __setitem__(self, k, v):
''' besides delegating to dict, we maintain self._rating '''
if k in self:
del self._rating[self.rating(k)] ##
dict.__setitem__(self, k, v)
insort_left(self._rating, (v, k))
def __delitem__(self, k):
''' besides delegating to dict, we maintain self._rating '''
del self._rating[self.rating(k)]
dict.__delitem__(self, k)
''' delegate some methods to dict explicitly to avoid getting
DictMixin's slower (though correct) implementations instead '''
__len__ = dict.__len__
__contains__ = dict.__contains__
has_key = __contains__
''' the key semantic connection between self._rating and the order
of self.keys( ) -- DictMixin gives us all other methods 'for
free', although we could implement them directly for slightly
better performance. '''
def __iter__(self):
for v, k in self._rating:
yield k
iterkeys = __iter__
def keys(self):
return list(self)
#the three ratings-related methods
def rating(self, key):
item = self[key], key
i = bisect_left(self._rating, item)
if item == self._rating[i]:
return i
raise LookUpError, "item not found in rating"
def getValueByRating(self, rating):
return self._rating[rating][0]
def getKeyByRating(self, rating):
return self._rating[rating][1]
def _test( ):
''' we use doctest to test this module, which must be named
rating.py, by validating all the examples in docstrings. '''
import doctest, rating
doctest.testmod(rating)
if __name__ == "__main__":
r = Ratings({"bob":30, "john":30})
print "r is"
print r
print "\n"
print "len(r) is"
print len(r)
print "\n"
print "updating with {'paul': 20, 'tom': 10} "
r.update({"paul": 20, "tom": 10})
print "\n"
print "now r is"
print r
print "\n"
print "r.has_key('paul') is"
print r.has_key("paul")
print "\n"
print " 'paul' in r is"
print ("paul" in r)
print "\n"
print "r.has_key('alex') is"
print r.has_key("alex")
print "\n"
print " 'alex' in r is"
print ("alex" in r)
print '\n'
print 'r is'
print r
print "changing john to '20' with 'r['john']= 20' doesn't work. "
r["john"]=20