python的dict()字典数据类型的方法详解以及案例使用

一、之前的回顾

# int 数字
# str 字符串
# list 列表
# tuple 元组
# dict 字典

字典中最重要的方法

keys()

values()

items()

get

update

字典是以 "key":"value" 的方式存储的

1、字典里面是键值对，每个元素之间也是用逗号分隔，是用{}大括号括起来的

字典里面的value可以是任何值，可以无限嵌套列表和元组

布尔值(不能跟0或1一起出现，当key里面没有0和1就可以做key)、列表、字典不能作为字典的key

字典是无序的，每次运行，输出的结果都不是固定的

二、下面了解下字典的常用操作

info = {"k1": "v1","k2": "v2"}
print (info)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k1': 'v1', 'k2': 'v2'}
info = {"k1": 18,"k2": True,"k3":[11,[],(),22,33,{"kk1":"vv1","kk2":"vv2","kk3":(11,22,),}],"k4":(11,22,33,44,)
}
print (info)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k2': True, 'k1': 18, 'k3': [11, 22, 33, {'kk3': (11, 22), 'kk2': 'vv2', 'kk1': 'vv1'}], 'k4': ()}

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2.数字、字符串、布尔值、元组、都可以做key

info = {2:"abc","k1":"def",True:"123",(11,22):"456"
}
print (info)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k1': 'def', True: '123', 2: 'abc', (11, 22): '456'}

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3.列表和字典都不能作为字典的key

（1）列表不能作为字典的key

info = {2:"abc","k1":"def",True:"123",[11,22]:"456"
}TypeError: unhashable type: 'list'

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（2）字典不能作为字典的key

info = {2:"abc","k1":"def",True:"123",{"k3":"v3"}:"456"
}TypeError: unhashable type: 'dict'

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4、字典去保存的时候是按照哈希表保存的

5、字典是无序的（发现每次打印结果都不一样，所以字典是无序的）

第一次打印

C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py

{'k2': True, 'k4': (11, 22, 33, 44), 'k1': 18, 'k3': [11, [], (), 22, 33, {'kk2': 'vv2', 'kk1': 'vv1', 'kk3': (11, 22)}]}

第二次打印

C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py

{'k4': (11, 22, 33, 44), 'k1': 18, 'k3': [11, [], (), 22, 33, {'kk1': 'vv1', 'kk2': 'vv2', 'kk3': (11, 22)}], 'k2': True}

6.按照key去取值，比如要取到18这个值应该怎么做（这里就不是索引的的0123这些了）

info = {"k1": 18,"k2": True,"k3":[11,[],(),22,33,{"kk1":"vv1","kk2":"vv2","kk3":(11,22,),}],"k4":(11,22,33,44,)
}
v = info["k1"]
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py18

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比如想要拿到99999这个值，就是下面这样写了（因为想拿3这个key对应的value，所以直接就写3这个数字就可以了，不用带双引号）

info = {"k1": 18,3: 99999,"k3": [11,[],(),22,33,{"kk1": "vv1","kk2": "vv2","kk3": (11, 22,),}],"k4": (11, 22, 33, 44,)
}
v = info[3]
print(v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py99999

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7、拿到11 这个元素该怎么写

第一步拿到k3这个key，结果就是一个列表了，想要拿到元组里面的那个11，就得先拿列表里面的整个字典的元素，位置是5

v = info["k3"]
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py[11, [], (), 22, 33, {'kk3': (11, 22), 'kk2': 'vv2', 'kk1': 'vv1'}]

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拿到列表里面的这个字典之后，要想取到元组里面的11，首先得拿到kk3这个key对应的value

v = info["k3"][5]
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'kk2': 'vv2', 'kk3': (11, 22), 'kk1': 'vv1'}

现在拿到这个元组了，想要元组里面的11这个元素就简单了，11位于这个元素的第0个位置

v = info["k3"][5]["kk3"]
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py(11, 22)

拿到元组中的11的这个元素了

v = info["k3"][5]["kk3"][0]
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py11

合起来就是下面这

info = {"k1": 18,3: 99999,"k3": [11,[],(),22,33,{"kk1": "vv1","kk2": "vv2","kk3": (11, 22,),}],"k4": (11, 22, 33, 44,)
}
v = info["k3"][5]["kk3"][0]
print(v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py11

8.删除字典中的key

info = {"k1": 18,3: 99999,"k3": [11,[],(),22,33,{"kk1": "vv1","kk2": "vv2","kk3": (11, 22,),}],"k4": (11, 22, 33, 44,)
}
del info["k1"]
print (info)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{3: 99999, 'k3': [11, [], (), 22, 33, {'kk1': 'vv1', 'kk2': 'vv2', 'kk3': (11, 22)}], 'k4': (11, 22, 33, 44)}

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9.删除kk1这个key

info = {"k1": 18,3: 99999,"k3": [11,[],(),22,33,{"kk1": "vv1","kk2": "vv2","kk3": (11, 22,),}],"k4": (11, 22, 33, 44,)
}
del info["k3"][5]["kk1"]
print (info)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k1': 18, 'k3': [11, [], (), 22, 33, {'kk3': (11, 22), 'kk2': 'vv2'}], 3: 99999, 'k4': (11, 22, 33, 44)}

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10、字典支持for循环，默认循环的时候只有key

info = {"k1": 18,3: 99999,"k3": [11,[],(),22,33,{"kk1": "vv1","kk2": "vv2","kk3": (11, 22,),}],"k4": (11, 22, 33, 44,)
}
for n in info:print (n)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyk13k3k4

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11.取字典里面的key，字典里面也有一个方法叫keys

info = {"k1": 18,3: 99999,"k3": [11,[],(),22,33,{"kk1": "vv1","kk2": "vv2","kk3": (11, 22,),}],"k4": (11, 22, 33, 44,)
}
# for n in info:
#     print (n)
v = info.keys()
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pydict_keys(['k1', 3, 'k4', 'k3'])

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12.取字典里面的values 有一个方法叫做value，可以结合一下for循环，一个一个的打印出来，为啥只有四行呢，因为key只有4个，这是对应的4个key的4个value

info = {"k1": 18,3: 99999,"k3": [11,[],(),22,33,{"kk1": "vv1","kk2": "vv2","kk3": (11, 22,),}],"k4": (11, 22, 33, 44,)
}
for n in info.values():print (n)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py99999[11, [], (), 22, 33, {'kk3': (11, 22), 'kk2': 'vv2', 'kk1': 'vv1'}](11, 22, 33, 44)18

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13.既想拿到key 又想拿到value（自己写for循环）

info = {"k1": 18,3: 99999,"k3": [11,[],(),22,33,{"kk1": "vv1","kk2": "vv2","kk3": (11, 22,),}],"k4": (11, 22, 33, 44,)
}
for n in info.keys():print (n,info[n])C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyk4 (11, 22, 33, 44)k3 [11, [], (), 22, 33, {'kk2': 'vv2', 'kk3': (11, 22), 'kk1': 'vv1'}]3 99999k1 18

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14、既拿到key又拿到value，字典有一个方法，items 我们用一下试试

因为是2个值，所以循环的时候，要用两个变量，这样items这个方法才会把key的值赋值给k，把value的值赋值给v，最后在打印k,v

info = {"k1": 18,3: 99999,"k3": [11,[],(),22,33,{"kk1": "vv1","kk2": "vv2","kk3": (11, 22,),}],"k4": (11, 22, 33, 44,)
}
for k,v in info.items():print (k,v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyk1 18k4 (11, 22, 33, 44)3 99999k3 [11, [], (), 22, 33, {'kk2': 'vv2', 'kk1': 'vv1', 'kk3': (11, 22)}]

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二、dict字典的方法详解

1、clear(self)

D.clear() -> None. Remove all items from D.

清空字典

D = {"11":"aa","22":"bb","33":"cc"}
v = D.clear()
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyNone

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2. copy(self) 浅拷贝

D = {"11":"aa","22":"bb","33":"cc"}
v = D.copy()
print (v)
print (D)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'22': 'bb', '11': 'aa', '33': 'cc'}{'22': 'bb', '11': 'aa', '33': 'cc'}

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3. fromkeys

根据序列，创建字典，并指定统一一个value作为key的值

Returns a new dict with keys from iterable and values equal to value

@staticmethod # known case   这是静态方法的意

def fromkeys(*args, **kwargs）

静态方法是这样使用的类名.方法

这个必须传2个参数，第一个参数是用来创建字典的key的，必须是可迭代对象，列表、元组，字符串都可以，第二个参数是这些key的统一的值

第一个参数是列表的方式

v = dict.fromkeys(["name","11","woai"],123)
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'woai': 123, '11': 123, 'name': 123}

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第一个参数是元组的方式

v = dict.fromkeys(("what","66","woai"),123)
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'woai': 123, '66': 123, 'what': 123}

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第一个参数是字符串的方式

v = dict.fromkeys("name",123)
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'m': 123, 'e': 123, 'n': 123, 'a': 123}

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4. get(self, k, d=None)

获取key的值

D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None.

我们通过这种方法的话，如果key不存在的话，程序就直接报错了

D = {"11":"aa","22":"bb","33":"cc"}
v = D["111"]
print (v)

KeyError: '111'

get这个方法在取值的时候，直接加key的名字就可以取到key的对应的值

D = {"k1":"v1","k2":"v2"}
v = D.get("k1")
print(v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyv1

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当要取的这个key不存在时，可以指定一个返回值，默认是None

D = {"k1":"v1","k2":"v2"}
v = D.get("k3")
print(v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyNone

当要取的这个key不存在时，指定一个固定的返回值

D = {"k1":"v1","k2":"v2"}
v = D.get("k3","000")
print(v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py000

5. items(self)

同时拿到key和value

D = {"k1":"v1","k2":"v2"}
for n in  D.items():print(n)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py('k2', 'v2')('k1', 'v1')

6. keys(self)

取出字典中的所有key

D = {"k1":"v1","k2":"v2"}
for n in  D.keys():print(n)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyk2k1

7. values(self）

取出字典里面的所有value

D = {"k1":"v1","k2":"v2"}
for n in  D.values():print(n)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyv2v1

8. pop(self, k, d=None)

删除指定的key

D = {"k1":"v1","k2":"v2"}
v = D.pop("k1")
print (D)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k2': 'v2'}

删除指定的key并把删除的value打印出来

D = {"k1":"v1","k2":"v2"}
v = D.pop("k1")       v就是指定删除的key  值是v1
print (D,v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k2': 'v2'} v1

当删除的指定的key不存在的时候，可以指定一个参数，让结果返回这个指定的参数

D = {"k1":"v1","k2":"v2"}
v = D.pop("k3","000")
print (D)
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k1': 'v1', 'k2': 'v2'}000

9.popitem(self)

随机删除一个key

被删除的key和value是以一个元组的方式输出的

D = {"k1":"v1","k2":"v2"}
v = D.popitem()
print (D)
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k2': 'v2'}('k1', 'v1')

也可以这样写

D = {"k1":"v1","k2":"v2"}
k,v = D.popitem()
print (D,k,v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k2': 'v2'} k1 v1

10. setdefault(self, k, d=None)

设置key对应的值，

如果参数里面的key已存在，则不设置，获取当前key对应的值

如果参数里面的key不存在，则设置key的值，获取当前key对应的值

当key存在的时候，则不设置，并且获取当前key的值

D = {"k1":"v1","k2":"v2"}
v = D.setdefault("k1","woaini")
print (D)
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k2': 'v2', 'k1': 'v1'}v1

当key不存在的时候，则增加一个key，并设置key的值，并返回参数中指定key的值

D = {"k1":"v1","k2":"v2"}
v = D.setdefault("k3","woaini")
print (D)
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k3': 'woaini', 'k2': 'v2', 'k1': 'v1'}woaini

11. update(self, E=None, **F)

如果key存在的话，就更新key的值，如果key不存在的话，就增加到字典里面

k1是在原来基础上修改的，k3是新增的

D = {"k1":"v1","k2":"v2"}
D.update({"k1":"333","k3":"666"})
print (D)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k3': '666', 'k2': 'v2', 'k1': '333'}

第二种写法：

D = {"k1":"v1","k2":"v2"}
D.update(k1=111,k3=666,k5="woaini")
print (D)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.py{'k2': 'v2', 'k5': 'woaini', 'k1': 111, 'k3': 666}

D.update(k1=111,k3=666,k5="woaini")

相当于在内部自动转换成一个字典，做个更新

如果参数里面是**kwargs  这样的，默认就会把

D.update(k1=111,k3=666,k5="woaini") 自动转换成字典

12.字典里面的in操作

（1）判断字典的key里面是否包含k1

只能判断key不能判断vlaue，想判断value怎么办呢，看（2）

D = {"k1":"v1","k2":"v2"}
v = "k1" in D
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyTrue

（2）判断字典里面的value是否包含v1

D = {"k1":"v1","k2":"v2"}
v = "v1" in D.values()
print (v)C:\python35\python3.exe D:/pyproject/day12列表/dict-way.pyTrue

转载于:https://www.cnblogs.com/gouguoqilinux/p/9126832.html