您正在尝试实现使用Python Cookbook（第二版）中的一个配方来为字典类型添加评级功能，却遇到错误：
AttributeError: 'Ratings' object has no attribute 'rating'
这个错误发生在您尝试更改键的“评级”时。
- 解决方案
错误的原因是编写配方的作者没有将以下代码段缩进一层，导致这些方法无法被识别为类方法：
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)
print "doc test?"
以下是缩进正确的代码：
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)
print "doc test?"
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
您需要使用正确的缩进代码来运行配方。
