python-010-Dictionary

Dictionary

键key：拼音值value：页码key-value:键值对字典是python中唯一的映射类型，指两个元素之间一一对应的关系（注明：字典是映射类型，不是序列类型）brand=[‘外星人‘，‘戴尔’，‘联想’，‘苹果’]English=[‘AlienWare‘,‘Dell‘,‘Lenovo‘,‘Apple‘]#品牌与英文一一对应print(‘外星人---‘,‘AlienWare‘)显示不出来中文，ASCII是十进制， 此时utf-8用的是Unicode，对应的是十六进制的数据，此时转换过程#不行，byteString,十进制,unicodeString 十六进制，python2默认十进制，

• Creation of dictionaries in Access

dict：字典可以dict(),n内置方法d={}表示形式d={‘外星人‘:‘AlienWare‘,‘戴尔‘:‘Dell‘,‘联想‘:‘Lenovo‘,‘苹果‘:‘Apple‘}print d[‘外星人‘]AlienWare

1. Name ={Key 1: value 1, key 2: Value 2, ... }
2. Empty Dictionary ={}
3. Create a dictionary with functions
Dict (mapping)

d=dict(((‘one‘,1),(‘two‘,2),(‘three‘,3)))#可以用列表 只要映射关系正确都可以print d#{‘three‘: 3, ‘two‘: 2, ‘one‘: 1}

4. Create a dictionary with keyword parameters

d=dict(one=1,two=2,three=3)print d#{‘three‘: 3, ‘two‘: 2, ‘one‘: 1}

• Access to Dictionaries
1. Name of dictionary [key name]
2, rewrite the value of the key corresponding

d=dict(one=1,two=2,three=3)d[‘one‘]=100print d#{‘three‘: 3, ‘two‘: 2, ‘one‘: 100}3、增加新的键值对d[‘four‘]=4print d#{‘four‘: 4, ‘three‘: 3, ‘two‘: 2, ‘one‘: 100}4、访问不存在的键值对：    报错    ·字典的内键方法（内置函数）：1、fromkeys(...)     创建并且返回一个新的字典    dict.fromkeys(s,[,v])        s：键 v:值（没有给值，默认None）当第一个参数是容器（元祖，列表，字典）时，会将第二个参数的整体看成键的值d.fromkeys((‘one‘,‘two‘,‘three‘))#{‘three‘: None, ‘two‘: None, ‘one‘: None}d.fromkeys([‘one‘,‘two‘,‘three‘])#{‘three‘: None, ‘two‘: None, ‘one‘: None}d.fromkeys({‘one‘:1,‘two‘:2,‘three‘:3})#{‘one‘: None, ‘three‘: None, ‘two‘: None}只拿键不拿值d.fromkeys([‘one‘,‘two‘,‘three‘],[1,2,3])#{‘three‘: [1, 2, 3], ‘two‘: [1, 2, 3], ‘one‘: [1, 2, 3]}

2. Keys ()
Returns a reference to a dictionary key

 d=d.fromkeys([‘one‘,‘two‘,‘three‘]) d.keys()#[‘three‘, ‘two‘, ‘one‘]（把所有键拿出了封装列表输出）3、values()d={‘one‘:1,‘two‘:2,‘three‘:3}d.values()#[3, 2, 1]    返回字典中的值引用（把所有值拿出了，封装一个列表返回）

4. Items ()

d.items()#[(‘three‘, 3), (‘two‘, 2), (‘one‘, 1)]返回字典的项（键值对）

5. Get (Key[,d])
Get (Access) a key value pair in a dictionary

 d.get(‘one‘)#1 d.get(‘five‘) print d.get(‘five‘)#None

6, In/not in

d={‘one‘:1,‘two‘:2,‘three‘:3}‘three‘in d#True‘five‘in d #False

7. Clear ()
Empty dictionary

d.clear()d#{}

8. Copy ()

浅拷贝字典拷贝，地址不同 开始字典里面内容没有发生改变，更深地址不变。

9. Pop ()
The given key pops up the corresponding key-value pair (the popup value is removed in the dictionary with no corresponding key
, and the dictionary does not have an exception, it will error. ) returns the corresponding value.

{‘three‘: 3, ‘two‘: 2, ‘one‘: 1}d.pop(‘one‘)#1

10, Popitem ()

同上，返回是一个键值对（栈空间）。d={‘three‘: 3, ‘two‘: 2, ‘one‘: 1}d.popitem()#(‘one‘, 1)弹出是随机的 内存上面的

11, SetDefault (...)
If there is no key-value pair in the dictionary, a key is created at random location, and if the value is not set, the default is None

setdefault(k,[,d])d={‘three‘: 3, ‘two‘: 2}d.setdefault(‘one‘)d#{‘one‘: None, ‘three‘: 3, ‘two‘: 2}

12, using dictionary mapping relationship, update the dictionary

d={‘three‘: 3, ‘two‘: 2, ‘one‘: 1}a={‘three‘:5}d.update(a)d#{‘one‘: 1, ‘three‘: 5, ‘two‘: 2}

python-010-Dictionary