python--字典dict

字典由多个键与其对应的值构成的对组成，是另一种可变容器模型，且可存储任意类型对象。字典的每个键值用冒号(:)分割，每个对之间用逗号(,)分割，整个字典包括在花括号({})中。

注：字典中的键是唯一的（其他类型的映射也是如此），而值不是唯一的。

字典类似于你通过联系人名字查找地址和联系人详细情况的地址簿.即，我们把键（名字）和值（详细情况）联系在一起。注意，键必须是唯一的，字典中的键/值对是没有顺序的(字典是无序的)。如果想要一个特定的顺序，那么应该在使用前自己对它们排序。字典是dict类的实例/对象。

字典是python中唯一的内建映射类型

1.dict 函数

使用dict 函数，通过其他映射（其他字典或键-值）这样的序列对建立字典

items = [("name","zhangsan"),("age",28),("job","educator")]
D = dict(items)
print (D)
print (type(D))

2. 字典的格式化字符串

一个电话本为例子的字典代码（引用格式化字符串）

phonebook = {
    "zhangsan":{
        "phone":"01012345",
        "addr":"tianhedong 32 hao",
    },
    "lisi":{
        "phone":"02023456",
        "addr":"huangpunan 54 hao",
    },
    "zhaowu":{
        "phone":"03034567",
        "addr":"tianhebei 17 hao",
    },
    "xiesen":{
        "phone":"06054321",
        "addr":"tianhexi 12 hao",
    },
}

labels ={
    "phone":"phone numbers",
    "addr":"address"
}

name = input ("please input your name:")

if "request" == "p" :key = "phone"
if "request" == "a" :key = "addr"
if name in phonebook :
    print ("%s's %s is %s." %(name, labels[key], phonebook[name][key]))

字典的方法

1. clear

clear 清除字典的所有项.类似list.sort ,无返回值

D = {}
D["name"] = "xieshengsen"
D["age"] = 25

print (D)

returned_value = D.clear()

print (D)
print (returned_value)

2. copy

copy 返回一个具有相同键值对的新字典（浅复制）

Q = {"username":"admin","machines":["foo","bar","baz"]}
QQ = Q.copy()
print (Q)
print (QQ)

QQ["username"] = "Administrator"
QQ["machines"].remove("bar")

print(Q)
print(QQ)

深复制

form copy import deepcopy

import copy

d = {}
d["names"] = ["hello","world"]

print (d)

dd = copy.copy(d)
dc = copy.deepcopy(d)
d["names"].append("haha")

print (d)
print (dd)
print(dc)

3. fromkeys

fromkeys 使用给定的键建立新的字典，每个键默认对应的值为none

print({}.fromkeys(["name","age"])) # none 作为默认值

print(dict.fromkeys(["name","age"]),"(unknown)") # 修改unknown 为默认值

4. get

get 更宽松的访问字典项的方法（一般来说，如果访问字典中不存在的项时会出错，使用get访问不会出现错误）

AA = {}
# print (AA["name"])  # 出现错误

print (AA.get("name"))  # 键值不存在,输出结果None

AA["name"]= "xieshengsen"
print (AA.get("name"))

5. items 和iteritems

items 方法将所有的字典项以列表方式返回，这些列表项中的每一项都是来自（键-值）。但是项在返回时并没有特殊的顺序。

II = {"title": "python web site","url":"https://www.python.org","spam":0}
print (II.items())

iteritems 会返回一个迭代器 而不是列表（python3 已经没有iteritems 这个方法）

6. keys 和iterkeys

keys 方法将字典的键以列表形式返回，而iterkeys 则返回针对键的迭代器

7. pop

pop 方法用来获取对应于给定的键的值，然后将这个键-值对从字典中移除

dd = {"hh":1,"yy":2,"vv":3,"gg":4}
print (dd.pop("hh"))
print (dd)

8. popitem

popitem 方法类似于list.pop，后者会弹出列表的最后一个元素。但，popitem弹出随机项，因为字典没有“最后元素”的概念（字典是无序的）.

p = {"url":"https://www.python.org/","spam":0,"title":"python web site"}
print (p.popitem())
print (p)

9. setdefault

setdefault 类似于get方法，能够获得与给定键相关联的值，setdefault还能在字典中不含有给定键的情况下设定相应的键值

set = {}
print (set.setdefault("name","N/A"))
print (set)

set["name"] = "zhangsan"
print (set.setdefault("name","N/A"))
print (set)

当键不存在时，setdefault 返回默认值并相应的更新字典，如果键存在，返回其相应值，但不改变字典。

10. update

update 方法是利用一个字典项更新另外一个字典.

up = {"color":"red","number":"1234","animal":"Bear","Fruits":"apples"}
da = {"Stationery":"book","food":"milk"}
up.update(da)
print (up)

提供的字典的项会被添加到旧字典中，相同的键会被覆盖

11. values

values 方法以列表的形式返回字典的值（itervalues 返回值的迭代器,python3 没有）,与返回值的列表不同的是，返回值列表中可以包含重复的元素。

valu = {}
valu[1]=1
valu[2]=2
valu[3]=3
valu[4]=1
print (valu.values())

字典dict官方解析

class dict(object):
    """
    dict() -> new empty dictionary
    dict(mapping) -> new dictionary initialized from a mapping object's
        (key, value) pairs
    dict(iterable) -> new dictionary initialized as if via:
        d = {}
        for k, v in iterable:
            d[k] = v
    dict(**kwargs) -> new dictionary initialized with the name=value pairs
        in the keyword argument list.  For example:  dict(one=1, two=2)
    """
    def clear(self): # real signature unknown; restored from __doc__
        """ D.clear() -> None.  Remove all items from D. """
        pass

    def copy(self): # real signature unknown; restored from __doc__
        """ D.copy() -> a shallow copy of D """
        pass

    @staticmethod # known case
    def fromkeys(*args, **kwargs): # real signature unknown
        """ Returns a new dict with keys from iterable and values equal to value. """
        pass

    def get(self, k, d=None): # real signature unknown; restored from __doc__
        """ D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None. """
        pass

    def items(self): # real signature unknown; restored from __doc__
        """ D.items() -> a set-like object providing a view on D's items """
        pass

    def keys(self): # real signature unknown; restored from __doc__
        """ D.keys() -> a set-like object providing a view on D's keys """
        pass

    def pop(self, k, d=None): # real signature unknown; restored from __doc__
        """
        D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
        If key is not found, d is returned if given, otherwise KeyError is raised
        """
        pass

    def popitem(self): # real signature unknown; restored from __doc__
        """
        D.popitem() -> (k, v), remove and return some (key, value) pair as a
        2-tuple; but raise KeyError if D is empty.
        """
        pass

    def setdefault(self, k, d=None): # real signature unknown; restored from __doc__
        """ D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D """
        pass

    def update(self, E=None, **F): # known special case of dict.update
        """
        D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
        If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]
        If E is present and lacks a .keys() method, then does:  for k, v in E: D[k] = v
        In either case, this is followed by: for k in F:  D[k] = F[k]
        """
        pass

    def values(self): # real signature unknown; restored from __doc__
        """ D.values() -> an object providing a view on D's values """
        pass

    def __contains__(self, *args, **kwargs): # real signature unknown
        """ True if D has a key k, else False. """
        pass

    def __delitem__(self, *args, **kwargs): # real signature unknown
        """ Delete self[key]. """
        pass

    def __eq__(self, *args, **kwargs): # real signature unknown
        """ Return self==value. """
        pass

    def __getattribute__(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

    def __getitem__(self, y): # real signature unknown; restored from __doc__
        """ x.__getitem__(y) <==> x[y] """
        pass

    def __ge__(self, *args, **kwargs): # real signature unknown
        """ Return self>=value. """
        pass

    def __gt__(self, *args, **kwargs): # real signature unknown
        """ Return self>value. """
        pass

    def __init__(self, seq=None, **kwargs): # known special case of dict.__init__
        """
        dict() -> new empty dictionary
        dict(mapping) -> new dictionary initialized from a mapping object's
            (key, value) pairs
        dict(iterable) -> new dictionary initialized as if via:
            d = {}
            for k, v in iterable:
                d[k] = v
        dict(**kwargs) -> new dictionary initialized with the name=value pairs
            in the keyword argument list.  For example:  dict(one=1, two=2)
        # (copied from class doc)
        """
        pass

    def __iter__(self, *args, **kwargs): # real signature unknown
        """ Implement iter(self). """
        pass

    def __len__(self, *args, **kwargs): # real signature unknown
        """ Return len(self). """
        pass

    def __le__(self, *args, **kwargs): # real signature unknown
        """ Return self<=value. """
        pass

    def __lt__(self, *args, **kwargs): # real signature unknown
        """ Return self<value. """
        pass

    @staticmethod # known case of __new__
    def __new__(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def __ne__(self, *args, **kwargs): # real signature unknown
        """ Return self!=value. """
        pass

    def __repr__(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    def __setitem__(self, *args, **kwargs): # real signature unknown
        """ Set self[key] to value. """
        pass

    def __sizeof__(self): # real signature unknown; restored from __doc__
        """ D.__sizeof__() -> size of D in memory, in bytes """
        pass

    __hash__ = None