写在前面

• 基于Python 3.7.2
• 环境：Anaconda 1.9.7
• 下次写集合
• 我多是通过例子来说明的，没有过多的阐述

1. 概览

列出dict的所有不含_的方法

for l1 in dir(dict):
    if "_" not in l1:
        print((l1))

clear
copy
fromkeys
get
items
keys
pop
popitem
setdefault
update
values

1. clear方法

清空

dict1={'country':'china','province':'jiangsu','code':'025'}
dict1.clear()
dict1

{}

2. copy

复制

dict1={'country':'china','province':'jiangsu','code':'025'}
dict2=dict1.copy()
dict2

{'country': 'china', 'province': 'jiangsu', 'code': '025'}

3. fromkeys 创建新字典

从一个可迭代的对象来创建一个字典，对象的元素作为key，values可以为空，否则就是默认值

help(dict.fromkeys)

Help on built-in function fromkeys:

fromkeys(iterable, value=None, /) method of builtins.type instance
    Create a new dictionary with keys from iterable and values set to value.

#fromkeys() 方法使用给定的多个 key 创建字典，这些 key 对应的 value 默认都是 None；
#也可以额外传入一个参数作为默认的 value。该方法一般不会使用字典对象调用（没什么意义），通常会使用 dict 类直接调用。
dict1=dict.fromkeys(['a','b'])
print(dict1)
dict2=dict.fromkeys(('c','d'))
print(dict2)
dict3=dict.fromkeys('e','001')
print(dict3)
dict4=dict.fromkeys(['f','g','h'],'002')
print(dict4)
dict5=dict.fromkeys('helloworld',23)
print(dict5)

{'a': None, 'b': None}
{'c': None, 'd': None}
{'e': '001'}
{'f': '002', 'g': '002', 'h': '002'}
{'h': 23, 'e': 23, 'l': 23, 'o': 23, 'w': 23, 'r': 23, 'd': 23}

4. get

通过key来得到字典的值，若无则会返回none，跟下标访问有区别

help(dict.get)

Help on method_descriptor:

get(self, key, default=None, /)
    Return the value for key if key is in the dictionary, else default.

dict1={'country':'china','province':'jiangsu','code':'025'}
print(dict1.get('code'))
print(dict1.get('not'))#未知的键值就返回none

025
None

5. items,keys,values

items:键值对
keys:键
values:值

help(dict.items)

Help on method_descriptor:

items(...)
    D.items() -> a set-like object providing a view on D's items

help(dict.keys)

Help on method_descriptor:

keys(...)
    D.keys() -> a set-like object providing a view on D's keys

help(dict.values)

Help on method_descriptor:

values(...)
    D.values() -> an object providing a view on D's values

dict1={'country':'china','province':'jiangsu','code':'025'}
print('******Keys Here******')
for k in dict1.keys():
    print(k)

print('******Values Here******')
for v in dict1.values():
    print(v)

print('******Items Here******')
for k,v in dict1.items():
    print(k,v)

******Keys Here******
country
province
code
******Values Here******
china
jiangsu
025
******Items Here******
country china
province jiangsu
code 025

6. pop

弹出指定的键，返回值
如果key不存在，返回指定的d，否则抛出KeyError

help(dict.pop)

Help on method_descriptor:

pop(...)
    D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
    If key is not found, d is returned if given, otherwise KeyError is raised

dict1={'country':'china','province':'jiangsu','code':'025'}
dict1.pop('code')
print(dict1)
print(dict1.pop('province1','hello'))
print(dict1)
dict1.pop('province1')

{'country': 'china', 'province': 'jiangsu'}
hello
{'country': 'china', 'province': 'jiangsu'}



---------------------------------------------------------------------------

KeyError                                  Traceback (most recent call last)

<ipython-input-11-2eeb48faedcc> in <module>
      4 print(dict1.pop('province1','hello'))
      5 print(dict1)
----> 6 dict1.pop('province1')


KeyError: 'province1'

7. popitem

1. 移除键值对，如果字典为空则抛出KeyError
2. 其实弹出"最后"一个键值对

help(dict.popitem)

Help on method_descriptor:

popitem(...)
    D.popitem() -> (k, v), remove and return some (key, value) pair as a
    2-tuple; but raise KeyError if D is empty.

#popitem
#popitem() 方法用于随机弹出字典中的一个 key-value 对
dict1={'country':'china','province':'jiangsu','code':'025'}
dict1.popitem()
print(dict1)
dict2={}
dict2.popitem()

{'country': 'china', 'province': 'jiangsu'}



---------------------------------------------------------------------------

KeyError                                  Traceback (most recent call last)

<ipython-input-15-4992ebb4170b> in <module>
      5 print(dict1)
      6 dict2={}
----> 7 dict2.popitem()


KeyError: 'popitem(): dictionary is empty'

8. setdefault

help(dict.setdefault)

Help on method_descriptor:

setdefault(self, key, default=None, /)
    Insert key with a value of default if key is not in the dictionary.
    
    Return the value for key if key is in the dictionary, else default.

1. 插入一个键，其值为给定的值，如果键在字典中不存在
2. 如果键在字典中存在，则返回其对应的值

dict1={'nanjing':'025','suzhou':'0512'}
print(dict1.setdefault('suzhou','0511'))
print(dict1.setdefault('zhenjiang','0511'))
print(dict1)

0512
0511
{'nanjing': '025', 'suzhou': '0512', 'zhenjiang': '0511'}

9. update

help(dict.update)

Help on method_descriptor:

update(...)
    D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
    If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]
    If E is present and lacks a .keys() method, then does:  for k, v in E: D[k] = v
    In either case, this is followed by: for k in F:  D[k] = F[k]

1. 通过字典或可迭代的对象来更新字典
2. 如果给出一个字典(或可迭代对象，存在keys方法)，则更新D的对应的键值（不论存在与否，存在就覆盖，不存在就插入）

dict1={'country':'china','province':'jiangsu','code':'025'}
dict2={'country':'china','province1':'jiangsu','code':'026'}#已存在的则更新，不存在的插入
dict1.update(dict2)
print(dict1)

{'country': 'china', 'province': 'jiangsu', 'code': '026', 'province1': 'jiangsu'}
{'country': 'china', 'province': 'jiangsu', 'code': '026', 'province1': 'jiangsu', 'loc': 'river'}
{'country': 'china', 'province': 'jiangsu', 'code': '026', 'province1': 'jiangsu', 'loc': 'river', 'age': 18}

3. 若果没有keys方法，那么...（不好解释看示例）

dict1={'country':'china','province':'jiangsu','code':'025'}
dict1.update(loc='river')
print(dict1)
dict1.update([('age',18)])
print(dict1)

{'country': 'china', 'province': 'jiangsu', 'code': '025', 'age': 18}

总结

---

十一个方法

• clear 清空
• copy 复制
• fromkeys 通过键来创建字典
• get 得到
• items 键值对
• keys 键
• pop 根据键弹出
• popitem 弹出
• setdefault 设置默认值
• update 更新
• values 值

---

查：keys、values、items、get
删：pop、popitem、clear
改：update
创建：setdefault 、fromkeys
其他：copy