Python的dict是无序的，这与C++不同，C++默认的map是有序的（基于tree的数据结构），C++ 11引入了unordered_map，实现了无序的map。而Python在collections目录中，有OrderedDict这个容器，可以实现有序的字典。

An OrderedDict is a dict that remembers the order that keys were first inserted. If a new entry overwrites an existing entry, the original insertion position is left unchanged. Deleting an entry and reinserting it will move it to the end.

代码示例如下：

from collections import OrderedDict
od=OrderedDict()
od['laoli']='laoli@163.com'
od['laozhang']='laozhang@gmail.com'
od['laomeng']='mengguang@gmail.com'

for k in od:
    print(k,od[k])

print()

d={}
d['laoli']='laoli@163.com'
d['laozhang']='laozhang@gmail.com'
d['laomeng']='mengguang@gmail.com'

for k in od:
    print(k,od[k])

参考资料：

http://docs.python.org/3/library/collections.html#collections.OrderedDict

http://www.cplusplus.com/reference/unordered_map/