Python3筆記019 - 4.4 字典

阿新 • • 發佈：2020-07-03

第4章序列的應用

python的資料型別分為：空型別、布林型別、數字型別、位元組型別、字串型別、元組型別、列表型別、字典型別、集合型別

在python中序列是一塊用於存放多個值的連續記憶體空間。

python內建了5種序列分別是元組、列表、字典、集合、字串。

本章將介紹元組、列表、字典、集合四種序列型別，字串將在第5章介紹

4.4 字典

字典的特徵：

1、通過鍵而不是通過索引來讀取

2、字典是可變的，並且可以任務巢狀

3、字典中的鍵必須唯一

4、字典中的鍵必須不可變

5、從3.6版本開始，是有序序列

4.4.1 字典的建立和刪除

1、直接使用{}建立字典

dictonary = {"key1":"value1", "key2":"value2", ..., "keyn":"valuen"}
 

引數說明

dictionary表示字典名稱

key1、key2、...keyn表示元素的鍵，必須唯一

value1、value2、...、valuen表示元素的值，不須唯一

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六","Sunday":"星期日",}
 

print(type(dict1))

output:

<class 'dict'>

dictionary = {} # 空字典

dictionary = dict() # 空字典

2、通過對映函式建立字典

dictionary = dict(zip(list1, list2))

引數說明

dictionary表示字典名稱

zip()函式用於將多個列表或元組對應位置的元素組合為元組，並返回包含這些內容的zip物件

list1 = ["星期一","星期二","星期三","星期四","星期五","星期六","星期日"]
 

list2 = ["Monday","Tuesday","wednesday","Thursday","Friday","Saturday","Sunday"]

dictionary = dict(zip(list1, list2))

print(type(dictionary))

print(dictionary)

output:

<class 'dict'>

{'星期一': 'Monday', '星期二': 'Tuesday', '星期三': 'wednesday', '星期四': 'Thursday', '星期五': 'Friday', '星期六': 'Saturday', '星期日': 'Sunday'}

3、通過給定的關鍵字引數建立字典

dictionary = dict(key1=value1, key2=value2, ..., keyn=valuen)

dictionary = dict(key1="value1", key2="value2", keyn="valuen")

print(type(dictionary))

print(dictionary)

output:

<class 'dict'>

{'key1': 'value1', 'key2': 'value2', 'keyn': 'valuen'}

4、刪除字典

del dictionary

dictionary.clear()

dictionary = dict(key1="value1", key2="value2", keyn="valuen")

del dictionary

print(dictionary)

output:

NameError: name 'dictionary' is not defined

dictionary = dict(key1="value1", key2="value2", keyn="valuen")

dictionary.clear()

print(dictionary)

output:

{}

4.4.2 通過鍵值對訪問字典

1、通過鍵訪問值

ditionary[key]

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六","Sunday":"星期日",}

print(dict1["Monday"])

output:

星期一

2、通過字典物件的get()方法

dictionary.get(key[,default])

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六","Sunday":"星期日",}

print(dict1.get("Monday"))

output:

星期一

4.4.3 遍歷字典

1、keys()

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六","Sunday":"星期日",}

for i in dict1.keys():

    print(i)

output:

Monday

Tuesday

wednesday

Thursday

Friday

Saturday

Sunday

2、values()

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六","Sunday":"星期日",}

for i in dict1.values():

    print(i)

output:

星期一

星期二

星期三

星期四

星期五

星期六

星期日

3、items()

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六","Sunday":"星期日",}

for i in dict1.items():

    print(i)

output:

('Monday', '星期一')

('Tuesday', '星期二')

('wednesday', '星期三')

('Thursday', '星期四')

('Friday', '星期五')

('Saturday', '星期六')

('Sunday', '星期日')

4.4.4 新增、修改、刪除字典元素

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六",}

# 新增

dict1["Sunday"]="星期日"

print(dict1)

output:

{'Monday': '星期一', 'Tuesday': '星期二', 'wednesday': '星期三', 'Thursday': '星期四', 'Friday': '星期五', 'Saturday': '星期六', 'Sunday': '星期日'}

# 修改

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六","Sunday":"星期日",}

dict1["Sunday"]="星期天"

print(dict1)

output:

{'Monday': '星期一', 'Tuesday': '星期二', 'wednesday': '星期三', 'Thursday': '星期四', 'Friday': '星期五', 'Saturday': '星期六', 'Sunday': '星期天'}

# 刪除

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六","Sunday":"星期日",}

del dict1["Sunday"]

# 如果要刪除的元素不存在，會丟擲異常，可以先做個判斷

dict1 = {"Monday":"星期一","Tuesday":"星期二","wednesday":"星期三","Thursday":"星期四","Friday":"星期五","Saturday":"星期六","Sunday":"星期日",}

if "Sunday" in dict1:

    del dict1["Sunday"]

print(dict1)

output:

{'Monday': '星期一', 'Tuesday': '星期二', 'wednesday': '星期三', 'Thursday': '星期四', 'Friday': '星期五', 'Saturday': '星期六'}

4.4.5 字典推導式

import random

randomdict = {i:random.randint(10,100) for i in range(1,5)}

print("生成的字典為：",randomdict)

output:

生成的字典為： {1: 41, 2: 40, 3: 45, 4: 10}

# 拓展：值最大的字典

def max_pairs(dic):

    if len(dic) == 0:

        return dic

    max_val = max(map(lambda v: v[1], dic.items()))

    return [item for item in dic.items() if item[1] == max_val]

r = max_pairs({'a': -10, 'b': 5, 'c': 3, 'd': 5})

print(r)  # [('b', 5), ('d', 5)]

# 拓展:合併兩個字典

def merge_dict2(dic1, dic2):

    return {**dic1, **dic2}  # python3.5後支援一行程式碼實現合併字典

merge_dict({'a': 1, 'b': 2}, {'c': 3})  # {'a': 1, 'b': 2, 'c': 3}

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