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
原文地址:https://www.cnblogs.com/meifei/p/11384562.html