字典键的特性：

1）键值的唯一性，如果同一个键被赋值两次，后一个值被保存

2）键必须不可变，所以可以用数字，字符串或者元组充当键，不能用列表作为键。

eg:

dict = {'name':"jiaozi", 'age':23, 'work':"jiaozi"}

print(dict)

del dict['age']

print(dict)

dict.clear()

print(dict)

del dict

dict2 = {('name',):"Google", 'Age':7}

print(dict2)

# dict3 = {['name']: "Google", 'Age': 7}

dict4 = dict2

dict5 = dict2.copy()

print(dict4is dict2)

print(dict5is dict2)

dict2['Age'] =8

print(dict2)

print(dict4)

print(dict5)

seq = ('name', 'age')

dict6 = dict.fromkeys(seq)

print("新的字典为：{0}".format(str(dict6)))

dict6 = dict.fromkeys(seq, 10)

print("新的字典为：{0}".format(str(dict6)))

print("age值为：{0}".format(dict6.get('age')))

print("job值为：{0}".format(dict6.get('job', 'warrenwell')))

print(dict6)

print("sex值为：{0}".format(dict6.setdefault('sex', 'male')))

print("新字典为：", dict6)