Python字典的详细解析

# 字典的创建方式
# 方式一 {key: value}
dict1 = {'one': 1, 'two': 2, 'three': 3}
print(dict1)

# 方式二 dict(zip(keys, values))
# dict([(k, v), (k, v)])
dict2 = dict([('one', 1), ('two', 2), ('three', 3)])
print(dict2)

# dict(((k, v), (k, v)))
dict3 = dict((('one', 1), ('two', 2), ('three', 3)))
print(dict3)

# 方式三 dict(key=value)
dict4 = dict(one=1, two=2, three=3)
print(dict4)

# 方式四 字典推导式
lst1 = ['one', 'two', 'three']
lst2 = [1, 2, 3]
dict5 = {lst1[i]: lst2[i] for i in range(len(lst1))}
print(dict5)

# 方式五 fromkeys
# 没有指定value，默认None
dict6 = dict.fromkeys(['k1', 'k2', 'k3'])
print(dict6) # {'k1': None, 'k2': None, 'k3': None}

# 指定value
dict7 = dict.fromkeys(['k1', 'k2', 'k3'], 'value')
print(dict7) # {'k1': 'value', 'k2': 'value', 'k3': 'value'}

# 有则不变，无则增加
dic1 = {'name': 'lucy', 'age': 18}
dic1.setdefault('age', 45) # {'name': 'lucy', 'age': 18}
dic1.setdefault('sex', '男') # {'name': 'lucy', 'age': 18, 'sex': '男'}

# 按照键删除键值对，有返回值
# 如果设置了第二个参数则无论字典中有无此键都不会报错
dic2 = {'name': 'lucy', 'age': 18}
ret2 = dic2.pop('age')
print(ret2) # 18
print(dic2) # {'name': 'lucy'}

dic3 = {'name': 'lucy', 'age': 18}
ret3 = dic3.pop('sex', '没有此键')
print(ret3) # 没有此键
print(dic3) # {'name': 'lucy', 'age': 18}

# 清空
dic4 = {'name': 'lucy', 'age': 18}
dic4.clear()
print(dic4) # {}

dic5 = {'name': 'lucy', 'age': 18, 'hobby_list': ['study', 'play', 'shopping']}

l1 = dic5.get('hobby_list')
print(l1) # ['study', 'play', 'shopping']

l2 = dic5.get('sex')
print(l2) # None

l3 = dic5.get('sex', '没有此键')
print(l3) # 没有此键

dic6 = {'name': 'lucy', 'age': 18, 'hobby_list': ['study', 'play', 'shopping']}

# 1. 特殊的数据类型，类似于列表，但是没有索引
print(dic6.keys(), type(dic6.keys())) # dict_keys(['name', 'age', 'hobby_list']) <class 'dict_keys'>

# 2. 可以转化成列表
l1 = list(dic6.keys())
print(l1) # ['name', 'age', 'hobby_list']

# 3. 循环遍历
for k in dic6.keys():
 print(k, end=',') # name,age,hobby_list,

for k in dic6:
 print(k, end=',') # name,age,hobby_list,

dic7 = {'name': 'lucy', 'age': 18, 'hobby_list': ['study', 'play', 'shopping']}

# 1. 特殊的数据类型，类似于列表，但是没有索引
print(dic7.values()) # dict_values(['lucy', 18, ['study', 'play', 'shopping']])

# 2. 可以转化成列表
print(list(dic7.values())) # ['lucy', 18, ['study', 'play', 'shopping']

# 3. 循环遍历
for val in dic7.values():
 print(val, end=',') # lucy,18,['study', 'play', 'shopping'],

dic8 = {'name': 'lucy', 'age': 18, 'hobby_list': ['study', 'play', 'shopping']}
print(dic8.items()) # dict_items([('name', 'lucy'), ('age', 18), ('hobby_list', ['study', 'play', 'shopping'])])

for it in dic8.items():
 print(it)
# ('name', 'lucy')
# ('age', 18)
# ('hobby_list', ['study', 'play', 'shopping'])

# 利用了元组的拆包
for key, value in dic8.items():
 print(key, value)
# name lucy
# age 18
# hobby_list ['study', 'play', 'shopping']

# 更新，有则覆盖，无则添加
# 1. 增加键值对
# 方式一：
dic9 = {'name': 'lucy', 'age': 18}
dic9.update(hobby='运动', hight=178)
print(dic9) # {'name': 'lucy', 'age': 18, 'hobby': '运动', 'hight': 178}

# 方式二：
dic10 = {'name': 'lucy', 'age': 18}
dic10.update([('hobby', '运动'), ('hight', 178)])
print(dic10) # {'name': 'lucy', 'age': 18, 'hobby': '运动', 'hight': 178}

# 方式三：
dic11 = {'name': 'lucy', 'age': 18}
dic12 = {'name': 'tom', 'hight': 178}
dic11.update(dic12)
print(dic11) # {'name': 'tom', 'age': 18, 'hight': 178}

# 2. 修改键所对应的值
dic13 = {'name': 'lucy', 'age': 18}
dic13.update(name='tom')
print(dic13) # {'name': 'tom', 'age': 18}

# 没有指定value，默认None
dict14 = dict.fromkeys(['k1', 'k2', 'k3'])
print(dict14) # {'k1': None, 'k2': None, 'k3': None}

# 指定value
dict14 = dict.fromkeys(['k1', 'k2', 'k3'], 'value')
print(dict14) # {'k1': 'value', 'k2': 'value', 'k3': 'value'}

# 浅拷贝
dict15 = dict(one=1, two=2, three=3)
dict16 = dict15.copy()
print(dict16)

# 随机删除字典中的一对 键和值
dict17 = dict(one=1, two=2, three=3)
a = dict17.popitem()
print(a)
print(dict17)