Python Dict笔记

• 1 初始化
• 2 字典视图和几何
• 3 排序字典键
  • 3.1 sort:
  • 3.2 sorted:
  • 3.3 注意
• 4 常用函数
  • 4.1 get()
  • 4.2 pop()
  • 4.3 udpate()
  • 4.4 del()
  • 4.5 clear()
  • 4.6 copy()

1 初始化

>>> d = dict(name='visaya', age=20)

>>> d = dict(zip(['name', 'age'], ['visaya', 20]))

#dict.fromkeys(listkeys, default=0) 把listkeys中的元素作为key均赋值为value，默认为0
>>> d = dict.fromkeys(['a', 'b'], 1)
>>> d
{'a': 1, 'b': 1}

2 字典视图和几何

dict.keys()类似信使可以进行交集和并集等集合操作（类似集合，因为不存在重复的项），但dict.values()不可以进行如上操作。

>>> k = d.keys()
>>> k
dict_keys(['a', 'b'])
>>> list(k)
['a', 'b']
>>> k | {'x': 3}
{'a', 'x', 'b'}
>>> k | {'x'}
{'a', 'x', 'b'}
>>> k | {'x', 'y'}
{'a', 'y', 'b', 'x'}
>>> k & {'x'}
set()
>>> v = d.values()
>>> v
dict_values([1, 2])
>>> v | {'x'}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for |: 'dict_values' and 'set'

3 排序字典键

两种方法:

3.1 sort:

>>> Ks = list(d.keys())
>>> Ks.sort()
>>> for k in Ks:
...     print(k, d[k])
... 
a 1
b 2

3.2 sorted:

>>> for k in sorted(d.keys()):
...     print(k, d[k])
... 
a 1
b 2

3.3 注意

>>> for k in list(d.keys()).sort():
...     print(k, d[k])
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not iterable

出错原因：
list.sort() list.append()函数都是对自身的操作，没有返回值，故需先将list(d.keys())的结果保存下来，在结果上进行sort()

4 常用函数

4.1 get()

D.get(k[, d])   => D[k] if k in D else d. d defaults to none.

4.2 pop()

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

4.3 udpate()

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

>>> d = dict(name='visaya', age=21)
>>> d1= {'age': 20, 'sex': 'male'}
>>> d2 = zip(['a', 'b'], [1, 2])

>>> d.update(d1)
>>> d
{'age': 20, 'name': 'visaya', 'sex': 'male'}
#for k in d1: d[k] = d1[k]

>>> d.update(d2)
>>> d
{'age': 20, 'name': 'visaya', 'sex': 'male'}
#for (k, v) in d2: d[k] = v

4.4 del()

del D[key]

4.5 clear()

4.6 copy()

Author: visaya <visayafan@gmail.com>

Date: 2011-08-03 22:32:26 CST

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