python数据类型之字典

python数据类型之字典

dict 

数据类型—字典dict

特性：无序，key-value的结构存储数据，查找速度快

key必须是可hash数据类型，且是唯一的,value可以是任意的。

官方帮助文档

1. Help on class dict in module builtins: 

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2.  

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3. class dict(object) 

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4. | dict() -> new empty dictionary 

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5. | dict(mapping) -> new dictionary initialized from a mapping object's 

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6. | (key, value) pairs 

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7. | dict(iterable) -> new dictionary initialized as if via: 

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8. | d = {} 

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9. | for k, v in iterable: 

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10. | d[k] = v 

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11. | dict(**kwargs) -> new dictionary initialized with the name=value pairs 

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12. | in the keyword argument list. For example: dict(one=1, two=2) 

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13. |  

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14. | Methods defined here: 

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15. |  

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16. | clear(...) 

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17. | D.clear() -> None. Remove all items from D. 

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18. |  

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19. | copy(...) 

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20. | D.copy() -> a shallow copy of D 

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21. |  

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22. | fromkeys(iterable, value=None, /) from builtins.type 

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23. | Returns a new dict with keys from iterable and values equal to value. 

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24. |  

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25. | get(...) 

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26. | D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None. 

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27. |  

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28. | items(...) 

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

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30. |  

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31. | keys(...) 

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

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33. |  

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34. | pop(...) 

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35. | D.pop(k[,d]) -> v, remove specified key and return the corresponding value. 

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36. | If key is not found, d is returned if given, otherwise KeyError is raised 

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37. |  

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38. | popitem(...) 

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39. | D.popitem() -> (k, v), remove and return some (key, value) pair as a 

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40. | 2-tuple; but raise KeyError if D is empty. 

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41. |  

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42. | setdefault(...) 

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43. | D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D 

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44. |  

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45. | update(...) 

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46. | D.update([E, ]**F) -> None. Update D from dict/iterable E and F. 

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47. | If E is present and has a .keys() method, then does: for k in E: D[k] = E[k] 

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48. | If E is present and lacks a .keys() method, then does: for k, v in E: D[k] = v 

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49. | In either case, this is followed by: for k in F: D[k] = F[k] 

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50. |  

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51. | values(...) 

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

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53. |  

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54. | ---------------------------------------------------------------------- 

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55. | Data and other attributes defined here: 

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56. |  

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57. | __hash__ = None 

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创建字典

字典的key必须是不可数据类型、且必须是唯一的
class dict(object)
| dict() -> new empty dictionary
| dict(mapping) -> new dictionary initialized from a mapping object's
| (key, value) pairs
| dict(iterable) -> new dictionary initialized as if via:
| d = {}
| for k, v in iterable:
| d[k] = v
| dict(**kwargs) -> new dictionary initialized with the name=value

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直接创建
>>> a = {'name':'james','age':25}
>>> a
{'name': 'james', 'age': 25}

通过dict创建
>>> a = ('name','alex'),('age', 38)
>>> a
(('name', 'alex'), ('age', 38))
>>> dict(a)
{'name': 'alex', 'age': 38}

关键字创建
>>> dict(name = 'alex',age = 38)
{'name': 'alex', 'age': 38}

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字典的方法

['clear', 'copy', 'fromkeys', 'get', 'items', 'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']

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增加

1. 存在就覆盖，不存在就覆盖 

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2. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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3. >>> dic1['high'] = 175 # 不存在key = 'high'才新增，如果存在就是覆盖 

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4. >>> dic1 

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5. {'name': 'james', 'age': 18, 'sex': 'male', 'high': 175} 
6. dic1.setdefalut(key,value)　　# 字典中存在key,不做任何改变，不存在就新增，value不指定时默认为None 

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7. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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8. >>> dic1.setdefault("name",'JAMES') # 字典中存在key为'name'的键值对，直接返回key对应的值，字典没有改变 

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9. 'james' 

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10. >>> dic1 

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11. {'name': 'james', 'age': 18, 'sex': 'male'}  
12. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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13. >>> dic1.setdefault('weight',130) # 字典中不存在key = 'weight',就新增进去，返回value 

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14. 130 

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15. >>> dic1 

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16. {'name': 'james', 'age': 18, 'sex': 'male', 'weight': 130} 

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删除

1. dic1.pop(key，x) 

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2. 指定key值删除，如果key存在，返回key对应的value,x缺失的情况下，key不存在会报错。指定x，key不存在返回x，不会报错。  
3. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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4. >>> dic1.pop('age') # 不指定x,key存在返回key的value 

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5. >>> dic1 

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6. {'name': 'james', 'sex': 'male'} 

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7. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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8. >>> dic1.pop("high") # 不指定x，key不存在报错 

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9. Traceback (most recent call last): 

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10. File "<pyshell#24>", line 1, in <module> 

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11. dic1.pop("high") 

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12. KeyError: 'high' 

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13. 如果指定了x,key不存在时，直接返回x；如果指定x,key存在就直接返回key对应的value（可设置返回值x） 

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14. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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15. >>> dic1.pop("high",178)  
16. dic1.popitem() # 随机删除，有返回值，返回以元组形式的键值。 

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17. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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18. >>> dic1.popitem() 

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19. ('sex', 'male') 

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20. del dic1.[key] # 按照指定的key删除键值，没有返回值，如果key不存在会报错 

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21. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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22. >>> del dic1.['heigh'] 

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23. SyntaxError: invalid syntax  
24. del dic1 # 直接删除字典 

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25. dic1.clear() #清空列表 

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修改

1. 赋值修改 

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2. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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3. >>> dic1['name'] = 'JAMES' # 直接对指定的key值对应的value进行赋值修改 

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4. >>> dic1 

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5. {'name': 'JAMES', 'age': 18, 'sex': 'male'} 
6. dic1.update(dic2) # 更新  

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7. 把dic2的键值对更新到dic1中，相同key值的，覆盖掉dic1中的value，dic1中的没有的key,新增进去 

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8. dic1法生改变，dic2不发生改变 

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9. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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10. >>> dic2 = {'name':'tony','heigh':178} 

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11. >>> dic1.update(dic2) 

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12. >>> dic1 

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13. {'name': 'tony', 'age': 18, 'sex': 'male', 'heigh': 178} 

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14. >>> dic2 

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15. {'name': 'tony', 'heigh': 178} 

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查询

1. 第一种：dic1[key] 按照指定的key，找出对应的value，如果key不存在，会报错 

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2. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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3. >>> dic1['name'] 

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4. 'james' 

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5. >>> dic1['high'] 

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6. Traceback (most recent call last): 

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7. File "<pyshell#43>", line 1, in <module> 

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8. dic1['high'] 

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9. KeyError: 'high'  
10. 第二种：dic1.get(key,x) 查找对应键的值，可设置返回值，x默认是None 

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11. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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12. >>> dic1.get('name') # 如果存在返回对应的value 

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13. 'james' 
14. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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15. >>> dic1.get('heigh','不存在') # 如果key不存在，返回x指定的值,x为空默认返回None 

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16. '不存在'  
17. dic1.keys() 返回字典里面的全部key，以列表的形式返回 

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18. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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19. >>> dic1.keys() 

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20. dict_keys(['name', 'age', 'sex'])  
21. dic1.values() 返回字典里面的全部value，以列表的形式返回 

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22. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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23. >>> dic1.values() 

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24. dict_values(['james', 18, 'male'])  
25. dic1.items() 把字典的键和值放进元组，以列表的形式返回 

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26. >>> dic1 = {'name':'james', 'age':18, 'sex':'male'} 

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27. >>> dic1.items() 

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28. dict_items([('name', 'james'), ('age', 18), ('sex', 'male')]) 

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字典的其他方法

fromkeys(iterable, value=None, /) method of builtins.type instance
Returns a new dict with keys from iterable and values equal to value.

1. >>> a = 'name' 

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2. >>> dict.fromkeys(a) 

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3. {'n': None, 'a': None, 'm': None, 'e': None} 

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4. >>> b = [21,22,23] 

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5. >>> dict.fromkeys(a,b) 

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6. {'n': [21, 22, 23], 'a': [21, 22, 23], 'm': [21, 22, 23], 'e': [21, 22, 23]} 

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复制

copy(...) method of builtins.dict instance
D.copy() -> a shallow copy of D
查看链接

字典的循环

>>> for index,k in enumerate(a):
    print(index,k)      
0 name
1 age
2 sex

>>> for k in a:
          print(k,a[k])      
name peiqi
age 38
sex male