python基础之字典dict

不可变数据类型：tuple、bool、int、str    --可哈希类型
可变数据类型：list、dict、set --不可哈希类型
dict-key 必须是不可变数据类型，可哈希
dict-value 任意数据类型
dict 优点：二分查找、存储大量的关系型数据
       特点：无序的-没有索引，只能按照键值对查找
增:dict[key] = value  dict.setdefault(key) dict.setdefault(key ,value)
删：dict.pop(key) dict.pop(key,returns) dict.popitem() dict.clear() del dict[key] del dict
改：dict[key] = value dict1.update(dict2)
查：dict[key] dict.get(key) dict.get(key,returns)
操作: for k in dict:  for k in dict.keys:  for k,v in dict.items
统计：len(tu1)
1，新增：
dict['key'] = value  --原dict无key值时，进行新增，有key值时，进行修改
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
dict1['key1'] = 'V1'
print(dict1)

result:{'key1': 'V1', 'key2': 'val2', 'key3': 'val3'}
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
dict1['key5'] = 'V1'
print(dict1)

result:{'key1': 'val1', 'key2': 'val2', 'key3': 'val3', 'key5': 'V1'}
dict.setdefault(key)--默认value为None
dict.setdefault(key，value) --原dict无key值时，进行新增，有key值时，不变
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
dict1.setdefault('key1')
print(dict1)

result:{'key1': 'val1', 'key2': 'val2', 'key3': 'val3'}
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
dict1.setdefault('key5')
print(dict1)

result:{'key1': 'val1', 'key2': 'val2', 'key3': 'val3', 'key5': None}
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
dict1.setdefault('key5','V5')
print(dict1)

result:{'key1': 'val1', 'key2': 'val2', 'key3': 'val3', 'key5': 'V5'}
2，删除：
dict.pop(key)--返回删除的值，如果dict中无key值-报错
dict.pop(key，返回值)--可设置返回值，存在key则删除，不存在则返回后面加的返回值
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
dict1.pop('key1')
print(dict1)

result:{'key2': 'val2', 'key3': 'val3'}
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
print(dict1.pop('key11','不存在key11'))

result:不存在key11
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
dict1.pop('key1','不存在key1')
print(dict1)

result:{'key2': 'val2', 'key3': 'val3'}
dict.popitem()--随机删除一个键值对，3.6版本按顺序删除,从后面开始删除
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
print(dict1.popitem())
print(dict1)

result:
('key3', 'val3')
{'key1': 'val1', 'key2': 'val2'}
dict.clear()--清空字典
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
print(dict1.clear())
print(dict1)

result:
None
{}
del dict/dict[key]
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
del dict1['key2']
print(dict1)

result:{'key1': 'val1', 'key3': 'val3'}
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
del dict1
print(dict1)

result:NameError: name 'dict1' is not defined
3，修改：
dict[key]=value --存在key时进行修改
dict1.update(dict2)--更新、覆盖添加
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
dict2 = {'k':'v','key1':'va1'}
dict1.update(dict2)
print(dict1)

result:{'key1': 'va1', 'key2': 'val2', 'key3': 'val3', 'k': 'v'}
4，查询：
dict[key]
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
print(dict1['key1'])

result:val1
dict.get(key,返回值)
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
print(dict1.get('key1'))

result:val1
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
print(dict1.get('key11'))

result:None
ey:

dict1 = {'key1':'val1','key2':'val2','key3':'val3'}
print(dict1.get('key11','不存在key'))

result:不存在key
5,计算长度

dict1= {'key1':'val1','key2':'val2','key3':'val3'}
print(len(dict1))

result:3