1.概述
字典是python中唯一的一个映射类型，以{}大括号括起来的键值对组成
字典中的key是唯一的，必须是可hash，不可变的数据类型
语法：{key1:value,key2:value}
#扩展：
可哈希（不可变）的数据类型：int,str,tuple,bool
不可哈希（可变）的数据类型：list,dict,set
#先来看看dict字典的源码写了什么，方法:按ctrl+鼠标左键点dict
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__ """ 清除内容 """ """ D.clear() -> None. Remove all items from D. """ pass def copy(self): # real signature unknown; restored from __doc__ """ 浅拷贝 """ """ D.copy() -> a shallow copy of D """ pass @staticmethod # known case def fromkeys(S, v=None): # real signature unknown; restored from __doc__ """ dict.fromkeys(S[,v]) -> New dict with keys from S and values equal to v. v defaults to None. """ pass def get(self, k, d=None): # real signature unknown; restored from __doc__ """ 根据key获取值，d是默认值 """ """ D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None. """ pass def has_key(self, k): # real signature unknown; restored from __doc__ """ 是否有key """ """ D.has_key(k) -> True if D has a key k, else False """ return False def items(self): # real signature unknown; restored from __doc__ """ 所有项的列表形式 """ """ D.items() -> list of D's (key, value) pairs, as 2-tuples """ return [] def iteritems(self): # real signature unknown; restored from __doc__ """ 项可迭代 """ """ D.iteritems() -> an iterator over the (key, value) items of D """ pass def iterkeys(self): # real signature unknown; restored from __doc__ """ key可迭代 """ """ D.iterkeys() -> an iterator over the keys of D """ pass def itervalues(self): # real signature unknown; restored from __doc__ """ value可迭代 """ """ D.itervalues() -> an iterator over the values of D """ pass def keys(self): # real signature unknown; restored from __doc__ """ 所有的key列表 """ """ D.keys() -> list of D's keys """ return [] def pop(self, k, d=None): # real signature unknown; restored from __doc__ """ 获取并在字典中移除 """ """ 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__ """ 获取并在字典中移除 """ """ 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__ """ 如果key不存在，则创建，如果存在，则返回已存在的值且不修改 """ """ 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 """ 更新 {'name':'alex', 'age': 18000} [('name','sbsbsb'),] """ """ D.update([E, ]**F) -> None. Update D from dict/iterable E and F. If E present and has a .keys() method, does: for k in E: D[k] = E[k] If E present and lacks .keys() method, 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__ """ 所有的值 """ """ D.values() -> list of D's values """ return [] def viewitems(self): # real signature unknown; restored from __doc__ """ 所有项，只是将内容保存至view对象中 """ """ D.viewitems() -> a set-like object providing a view on D's items """ pass def viewkeys(self): # real signature unknown; restored from __doc__ """ D.viewkeys() -> a set-like object providing a view on D's keys """ pass def viewvalues(self): # real signature unknown; restored from __doc__ """ D.viewvalues() -> an object providing a view on D's values """ pass def __cmp__(self, y): # real signature unknown; restored from __doc__ """ x.__cmp__(y) <==> cmp(x,y) """ pass def __contains__(self, k): # real signature unknown; restored from __doc__ """ D.__contains__(k) -> True if D has a key k, else False """ return False def __delitem__(self, y): # real signature unknown; restored from __doc__ """ x.__delitem__(y) <==> del x[y] """ pass def __eq__(self, y): # real signature unknown; restored from __doc__ """ x.__eq__(y) <==> x==y """ pass def __getattribute__(self, name): # real signature unknown; restored from __doc__ """ x.__getattribute__('name') <==> x.name """ pass def __getitem__(self, y): # real signature unknown; restored from __doc__ """ x.__getitem__(y) <==> x[y] """ pass def __ge__(self, y): # real signature unknown; restored from __doc__ """ x.__ge__(y) <==> x>=y """ pass def __gt__(self, y): # real signature unknown; restored from __doc__ """ x.__gt__(y) <==> x>y """ 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): # real signature unknown; restored from __doc__ """ x.__iter__() <==> iter(x) """ pass def __len__(self): # real signature unknown; restored from __doc__ """ x.__len__() <==> len(x) """ pass def __le__(self, y): # real signature unknown; restored from __doc__ """ x.__le__(y) <==> x<=y """ pass def __lt__(self, y): # real signature unknown; restored from __doc__ """ x.__lt__(y) <==> x<y """ pass @staticmethod # known case of __new__ def __new__(S, *more): # real signature unknown; restored from __doc__ """ T.__new__(S, ...) -> a new object with type S, a subtype of T """ pass def __ne__(self, y): # real signature unknown; restored from __doc__ """ x.__ne__(y) <==> x!=y """ pass def __repr__(self): # real signature unknown; restored from __doc__ """ x.__repr__() <==> repr(x) """ pass def __setitem__(self, i, y): # real signature unknown; restored from __doc__ """ x.__setitem__(i, y) <==> x[i]=y """ pass def __sizeof__(self): # real signature unknown; restored from __doc__ """ D.__sizeof__() -> size of D in memory, in bytes """ pass __hash__ = None dict
#演示什么数据类型能作为key
# dic = {'name':'guoke','age':22} #字符串可以为键(key) # dic = {1:'a',2:'b',3:'c'} #数字可以为键 # dic = {True:'1',False:'2'} #布尔值可以为键 # dic = {(1,2,3):'abc'} #元组也可以为键 # dic = {[1,2,3]:'abc'} #列表不能为键{key:vaule}
2.字典的增删改查
#2.1增加
#关键字 # 1、setdefault('键','值') # 2、变量['key'] = 'value'
#例子:
dic = {'广东':'广州','山东':'济南','海南':'三亚'}
dic['湖南'] = '长沙' #新增，前面是key,后面是值
print(dic)
#{'广东': '广州', '山东': '济南', '海南': '三亚', '湖南': '长沙'}
dic.setdefault('广西','桂林')
# 使用setdefault需要注意的是如果在字典中存在就不进行任何操作，不存在就进行添加
print(dic)
#{'广东': '广州', '山东': '济南', '海南': '三亚', '广西': '桂林'}
#2.2删除
#关键字 1、pop() 2、del dic[''] # 3、clear() #清空 4、popitem #随机删除 5、要注意的是字典没有remove这个删除命令
#例子：
dic = {'广东':'广州','山东':'济南','海南':'三亚'}
ret = dic.pop('广东') #通过key删除，返回被删除的value
print(ret) #广州 :可以查看到的是通过key将值为广州删除了
print(dic) #{'山东': '济南', '海南': '三亚'}
del dic['山东'] #要注意删的时候只能是写key，不能写value删
print(dic) #{'广东': '广州', '海南': '三亚'}
dic.clear() #{} #清空
print(dic) #{}
ret = dic.popitem() #随机删除，返回值 一个元组（key,value）
print(ret) #('海南', '三亚')
print(dic) #{'广东': '广州', '山东': '济南'}
#2.3.修改
#关键字 1、dic['键'] = '值' 2、dic.update(dic1)
#例子:
dic = {'广东':'广州','山东':'济南','海南':'三亚'}
dic["广东"] = '湖北'
#需要注意的是前边的修改是键key，然后等号后面修改的value值
print(dic) #{'广东': '湖北', '山东': '济南', '海南': '三亚'}
dic1 = {'战狼':'吴京','亮剑':'李云龙','山东':'淮上'}
dic.update(dic1)
print(dic)
#{'广东': '湖北', '山东': '淮上', '海南': '三亚', '战狼': '吴京', '亮剑': '李云龙'}
#把dic1中的内容更新到dic中，如果key重名，则修改替换，如果不存在key，则新增
#2.4.查询
# 关键字 # 1、使用for循环获取，获取到的是键，不是值 # 2、print(dic['']) #查询键，返回值 # 3、print(dic.get('')) #如果没有查询到的话就会返回None # 4、print(dic.setdefault(''))
#例子：
dic = {'广东':'广州','山东':'济南','海南':'三亚'}
# for i in dic:
# print(i) #for循环默认是获取字典中的键
# 广东
# 山东
# 海南
print(dic['广东']) #查看1，如果没有这个键的时候查询就会报错
# print(dic['湖北']) #报错，NameError: name '湖北' is not defined
print(dic.get('广东','这个是没有的')) #查看2，没有返回None，可以指定返回内容
#广州
print(dic.get('广西')) #None，因为没有这个key
print(dic.setdefault('广东')) #如果没有的话也是返回None
#2.5.字典的其他操作(特有)
#keys #获取到字典中的每一个键 #value #获取到字典中的值 #itmes #获取到字典中的键值对数据
#例子：
dic = {"id":123,"name":"cw","age":22,"ok":"大佬"}
print(dic.keys()) #(高仿列表)
for i in dic.keys():
print(i)
#获取到键:id，name,age,ok
for i in dic:
print(i) #以上的几种方法都是获取到字典中的每一个键
#获取到id，name,age,ok
print(dic.values())
for i in dic.values(): #获取到字典中的每一个值
print(i)
#获取到值：123，cw,22,大佬
for i in dic.items(): #获取到键值对
print(i)
# ('id', 123)
# ('name', 'cw')
# ('age', 22)
# ('ok', '大佬')
3.字典的嵌套
嵌套就是一层套着一层，字典套着字典
#演练：
#写字典嵌套来查找 dic1 = { "name": "张世豪", "age": 18, "wife": { "name": '大哥成', "age": 28 }, "children": ['第⼀个毛孩子', '第⼆个毛孩子'], "desc": '峰哥不不会告我吧. 没关系. 我想上头条的' } #通过key取查找，使用get #1.查找大哥成 #思路：首先可以看到大哥成是作为wife键的值，所以可以先找wife键,拿到值，再接着获取键name,打印出它的value值 print(dic1.get("wife")) #{'name': '大哥成', 'age': 28} print(dic1.get("wife").get("name")) #大哥成 #2.查看28 #思路：和上面一样，通过找出键获取到值 print(dic1.get("wife").get("age")) #28 #3.查找第一个毛孩子 #思路：同样是通过键找出值，然后通过索引进行获取 print(dic1.get("children")[0]) #第⼀个毛孩子
#嵌套练习
dic1 = { 'name':['guo',2,3,5], 'job':'teacher', 'dianshi':{'haijun':['python1','python2',100]} } #要求 # 1，将name对应的列表追加⼀个元素’ke’。 # 2，将name对应的列表中的guo首字母大写。 # 3，dianshi对应的字典加一个键值对’蒋小鱼’,’niubi’。 # 4，将dianshi对应的字典中的haijun对应的列表中的python2删除 # s1 = (dic1.get('name')) s1.append('ke') print(s1) #['guo', 2, 3, 5, 'ke'] print(dic1.get('name')[0].capitalize()) #Guo dic1['蒋小鱼'] = 'niubi' print(dic1) #{'name': ['guo', 2, 3, 5], 'job': 'teacher', 'dianshi': {'huijun': ['python1', 'python2', 100]}, '蒋小鱼': 'niubi'} dic2 = (dic1.get('dianshi').get('haijun').pop(1)) print(dic2) #python2 print(dic1) #{'name': ['guo', 2, 3, 5], 'job': 'teacher', 'dianshi': {'haijun': ['python1', 100]}}