概念：可用于循环就是迭代

#!/usr/bin/python

dic = {'a':1, 'b':2, 'c':3, 'd':4};
for key in dic:
    print "key:", key;

for value in dic.itervalues():
    print "value:", value;

for key in dic.iterkeys():
    print "key:", key;

for key in dic.keys():
    print "keys:", key;

for key,value in dic.iteritems():
    print "iteritems:", key, value;

#check 检查dic是否为可迭代类型
from collections import Iterable  #申明Iterable
print isinstance(dic, Iterable);

#enumerate
for x, y in enumerate(['a', 'b', 'c']):
    print x, y

for x,y in [(1, 2), (3, 4), (5, 6)]:
    print x,y

for x in [(1, 2), (3, 4), (5, 6)]:
    print x