Python之字典方法

1. 字典由键值对组成，且字典是无序的，可以进行嵌套 - dict，字典的value可以是任意类型

dict1 = {
    "k1": 'test',
    "k2": 1234,
    "k3": None,
    "k4": True,
    "k5": [1,2,3],
    "k6": {"a": 6,"b": "boc"},
    "k7": (1,2,3)
}

2. 字典的key，不能是列表(list是动态的 )，不能是字典

dict2 = {
    1: 'a',
    "b": 'c',
    # (1,2): None,
    [3,4]: True,
    {'d': 3,"e": "f"}: 3
}
当key为列表/字典时:
Traceback (most recent call last):
  File "D:/Project/pythonProject/pythonProject/Mytest3/test_a.py", line 19, in <module>
    dict2 = {
TypeError: unhashable type: 'list'

3. 通过key获取value，并通过索引获取到想要的值  -- * 不能通过切片方式查找(字典是无序的！)

dict3 = {
    "k1": 'test',
    "k2": 1234,
    "k3": None,
    "k4": True,
    "k5": [1,2,3],
    "k6": {"a": 6,"b": "boc","c": [1,2,3]},
    "k7": (1,2,3)
}
print(dict1["k6"]["c"][2])
结果：3

4. 使用del ，删除某个值 - 支持删除

dict4 = {
    "k1": 'test',
    "k2": 1234,
    "k3": None,
    "k4": True,
    "k5": [1,2,3],
    "k6": {"a": 6,"b": "boc","c": [1,2,3]},
    "k7": (1,2,3)
}
del dict4["k3"]
print(dict4)
结果：
{
	'k1': 'test',
	'k2': 1234,
	'k4': True,
	'k5': [1, 2, 3],
	'k6': {
		'a': 6,
		'b': 'boc',
		'c': [1, 2, 3]
	},
	'k7': (1, 2, 3)
}

5. 支持for循环，分别获取key和value

dict5 = {    
    "k1": 'test',
    "k2": 1234,
    "k3": None,
    "k4": True,
    "k5": [1,2,3],
    "k6": {"a": 6,"b": "boc","c": [1,2,3]},
    "k7": (1,2,3)
}

for item in dict5:
    print(item)
结果：输出的是字典的key - 默认

for item in dict5.values:
    print(item)
结果：输出为字典的value

for key,value in dict5.items():
　　print(key)
　　print(value)
结果：分别输出地点的key和value

6. fromkeys(*args, **kwargs) - 根据序列，创建字典，并指定统一的值

dict5 = {
    "k1": 'test',
    "k2": 1234,
    "k3": None,
    "k4": True,
    "k5": [1,2,3],
    "k6": {"a": 6,"b": "boc","c": [1,2,3]},
    "k7": (1,2,3)
}
print(dict5.fromkeys([1,"test",3],'t'))
结果：{1: 't', 'test': 't', 3: 't'}

7. get(), 根据key获取值，如果传入的key存在，则返回key的value；如果key不存在，则返回设置的值：111，或者未设置值则返回None

dict5 = {
    "k1": 'test',
    "k2": 1234,
    "k3": None,
    "k4": True,
    "k5": [1,2,3],
    "k6": {"a": 6,"b": "boc","c": [1,2,3]},
    "k7": (1,2,3)
}
v1 = dict5.get('k5',111)
print(v2)
结果：[1,2,3]

8. items，获取字典的key和value，keys()和values() 可以分别获取字典的key和value

for key,value in dict5.items():
　　print(key)
　　print(value)
结果：分别输出字典的key和value

9. pop() - 传入需要删除的key，如果传入的key存在，则返回对应的key的value，如果不存在则返回设置的值9

dict6 = {
    "k1": 'test',
    "k2": 1234,
    "k3": [1,2,'a']
}
v = dict6.pop('k3', 9)
print(v)
print(dict6)  - 得到需要删除的key的value
结果：
[1, 2, 'a']
{'k1': 'test', 'k2': 1234}

10. popitem() 随机删除一个键值对

dict6 = {
    "k1": 'test',
    "k2": 1234,
    "k3": [1,2,'a']
}
k,v = dict6.popitem()
print(k,v)
print(dict6)
结果：
k3 [1, 2, 'a']
{'k1': 'test', 'k2': 1234}

11. setdefault()　传入的key存在：获取传入key的value；若传入的key不存在，则可以设置对应的value

dict6 = {
    "k1": 'test',
    "k2": 1234,
    "k3": [1,2,'a']
}
v = dict6.setdefault('k111','test')
print(v,dict6)
结果：test {'k1': 'test', 'k2': 1234, 'k3': [1, 2, 'a'], 'k111': 'test'}

12. update()    更新字典add

dict6 = {
    "k1": 'test',
    "k2": 1234,
    "k3": [1,2,'a']
}
dict6.update({"k4": 123,"test":[1,2,'d']})
print(dict6)
结果：{'k1': 'test', 'k2': 1234, 'k3': [1, 2, 'a'], 'k4': 123, 'test': [1, 2, 'd']}