迭代defaultdict词典的键和值

Question

以下按预期工作:

d = [(1,2), (3,4)]
for k,v in d:
  print "%s - %s" % (str(k), str(v))

但这失败了:

d = collections.defaultdict(int)
d[1] = 2
d[3] = 4
for k,v in d:
  print "%s - %s" % (str(k), str(v))

附:

Traceback (most recent call last):  
 File "<stdin>", line 1, in <module>  
TypeError: 'int' object is not iterable 

为什么？我该如何解决？

Answer 1

你需要迭代dict.iteritems():

for k,v in d.iteritems():               # will become d.items() in py3k
  print "%s - %s" % (str(k), str(v))

Answer 2

如果您使用的是Python 3.6

from collections import defaultdict

for k, v in d.items():
    print(f'{k} - {v}')