数据类型之字典介绍

d={‘k1‘:111,(1,2,3):222} # d=dict(...)
print(d[‘k1‘])
# 111
print(d[(1,2,3)])
# 222
print(type(d))
# <class ‘dict‘>
?
d={} # 默认定义出来的是空字典
print(d,type(d))
# {} <class ‘dict‘>

d = dict(x=1, y=2, z=3)
print(d, type(d))
# {‘x‘: 1, ‘y‘: 2, ‘z‘: 3} <class ‘dict‘>

info = [
    [‘name‘, ‘egon‘],
    (‘age‘, 18),
    [‘gender‘, ‘male‘]
]
d = {}
for k, v in info:  # k,v=[‘name‘,‘egon‘],
    d[k] = v
print(d)
# {‘name‘: ‘egon‘, ‘age‘: 18, ‘gender‘: ‘male‘}
info = [
    [‘name‘, ‘egon‘],
    (‘age‘, 18),
    [‘gender‘, ‘male‘]
]
res=dict(info) # 一行代码搞定上述for循环的工作
print(res)
# {‘name‘: ‘egon‘, ‘age‘: 18, ‘gender‘: ‘male‘}

keys=[‘name‘,‘age‘,‘gender‘]
# d={}
# for k in keys:
#     d[k]=None
# print(d)
d={}.fromkeys(keys,None) # 一行代码搞定上述for循环的工作
print(d)
?

pyinfo = [
    [‘name‘, ‘egon‘],
    (‘age‘, 18),
    [‘gender‘, ‘male‘]
]
res=dict(info) 
print(res)
?
# {‘name‘: ‘egon‘, ‘age‘: 18, ‘gender‘: ‘male‘}
 

d={‘k1‘:111}
?
# 针对赋值操作：如果key存在，则修改
d[‘k1‘]=222
?
# 针对赋值操作：如果key不存在，则创建新值
d[‘k2‘]=3333
?
print(d)
# {‘k1‘: 222, ‘k2‘: 3333}

d={‘k1‘:111,‘k2‘:2222,‘k1‘:3333,‘k1‘:4444}
print(len(d))
# 4

d={‘k1‘:111,‘k2‘:2222}
print(‘k1‘ in d)
# True
print(111 in d)         # 只检测key
# False
 

d={‘k1‘:111,‘k2‘:2222}
del d[‘k1‘]
print(d)

d={‘k1‘:111,‘k2‘:2222}
res=d.pop(‘k2‘)
print(d)
print(res)

d={‘k1‘:111,‘k2‘:2222}
res=d.popitem()
print(d)
# {‘k1‘: 111}
?
print(res)
# (‘k2‘, 2222)

d={‘k1‘:111,‘k2‘:2222}
?
d.keys()
[‘k2‘, ‘k1‘]
d.values()
[2222, 111]
d.items()
[(‘k2‘, 2222), (‘k1‘, 111)]
dict(d.items())
{‘k2‘: 2222, ‘k1‘: 111}

d={‘k1‘:111,‘k2‘:2222}
for k in d.keys():
    print(k)
# k1
# k2
?
for k in d:
    print(k)
# k1
# k2
?
for v in d.values():
    print(v)
# 111
# 2222
?
for k,v in d.items():
    print(k,v)
# k1 111
# k2 2222
?
print(list(d.keys()))
# [‘k1‘, ‘k2‘]
print(list(d.values()))
# [111, 2222]
print(list(d.items()))
# [(‘k1‘, 111), (‘k2‘, 2222)]

d = {‘k1‘: 111}
d.clear()
print(d)
# {}
 

d={‘k1‘:111}
d.update({‘k2‘:222,‘k3‘:333,‘k1‘:111111111111111})
print(d)
# {‘k1‘: 111111111111111, ‘k2‘: 222, ‘k3‘: 333}

d={‘k1‘:111}
print(d[‘k2‘])  # key不存在则报错
# KeyError: ‘k2‘
?
print(d.get(‘k1‘)) 
# 111
?
print(d.get(‘k2‘)) 
# key不存在不报错，返回None

info={}
if ‘name‘ in info:
    ... # 等同于pass
else:
    info[‘name‘]=‘egon‘
print(info)
# {‘name‘: ‘egon‘}
?
?
?
?
?
info = {}
info.setdefault("name", "???")
print(info)
# {‘name‘: ‘???‘}

info = {"name": "wu"}
print(info.setdefault("name", "???"))
# wu
?
print(info)
# {‘name‘: ‘wu‘}

info = {}
print(info.setdefault("name", "???"))
# ???
?
print(info)
# {‘name‘: ‘???‘}