字典映射{ ：}

print(key，aDict[key])相当于名字和内容

#print语句默认每行添加一个换行符，所以：

>>> a={'host':'earth'}
>>> a['port']=80
>>> a
{'host': 'earth', 'port': 80}
>>> a('port')=80
SyntaxError: can't assign to function call
>>> a{'port'}=80
SyntaxError: invalid syntax
>>> a['port']=80
>>> a
{'host': 'earth', 'port': 80}
>>> a.keys()
dict_keys(['host', 'port'])
>>> a keys()
SyntaxError: invalid syntax
>>> keys()
Traceback (most recent call last):
  File "<pyshell#158>", line 1, in <module>
    keys()
NameError: name 'keys' is not defined
>>> a.keys( )
dict_keys(['host', 'port'])
>>> a.key()
Traceback (most recent call last):
  File "<pyshell#160>", line 1, in <module>
    a.key()
AttributeError: 'dict' object has no attribute 'key'
>>>