python3.x 基础一：dict字典

字典，{key,value}

help(dict)

• 定义一个字典：

>>> dict1
{'salary': '', 'age': '', 'name': 'yzw'}
>>> dict2=dict1
>>> id(dict2)
139948810542280
>>> id(dict1)
139948810542280
>>> dict2=dict1.copy()
>>> id(dict1),id(dict2)
(139948810542280, 139948887698696)

• |  clear(...)  清空一个字典
   |      D.clear() -> None.  Remove all items from D.

  >>> dict2.clear()
  >>> dict2
  {}

• |  copy(...)  普通赋值指向相同的内存地址
   |      D.copy() -> a shallow copy of D

  >>> dict2=dict1.copy()
  >>> id(dict1),id(dict2)
  (139948810542280, 139948887698696) 

• |  fromkeys(iterable, value=None, /) from builtins.type  创建一个以序列为key，值相同的字典
   |      Returns a new dict with keys from iterable and values equal to value.

  >>> seq1=('length','width','square')
  >>> dict3=dict.fromkeys(seq1)
  >>> dict3
  {'length': None, 'width': None, 'square': None}
  >>> dict4=dict.fromkeys(seq1,10)
  >>> dict4
  {'length': 10, 'width': 10, 'square': 10}

• |  get(...)  根据key取value，key不存在则返回None   dict[key]取值key不存在时报错
   |      D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None.

  >>> dict1
  {'salary': '', 'age': '', 'name': 'yzw'}
  >>> dict1.get('salary')
  ''
  >>> dict1.get('sex')
  >>> dict1['salary']
  '100'
  >>> dict1['sex']
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  KeyError: 'sex'

• |  items(...)  以列表返回可遍历的(键, 值) 元组数组
   |      D.items() -> a set-like object providing a view on D's items

  >>> dict1.items()
  dict_items([('salary', ''), ('age', ''), ('name', 'yzw')])  

• |  keys(...)  返回所有key的列表
   |      D.keys() -> a set-like object providing a view on D's keys

  >>> dict1.keys()
  dict_keys(['salary', 'age', 'name'])   

• |  pop(...)  删除字典给定键 key 所对应的值，返回值为被删除的值。key值必须给出。 否则，返回default值
   |      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.pop('salary')
  ''
  >>> dict1
  {'age': '', 'name': 'yzw'}
  >>> dict1.pop('sex')
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  KeyError: 'sex'
  >>> dict1['sex']='man'
  >>> dict1
  {'sex': 'man', 'age': '18', 'name': 'yzw'}

• |  popitem(...) 随机删除一个k/v
   |      D.popitem() -> (k, v), remove and return some (key, value) pair as a
   |      2-tuple; but raise KeyError if D is empty.

  >>> dict1
  {'square': None, 'kind': 'human', 'width': None, 'name': 'yzw', 'length': None, 'sex': 'man', 'age': ''}
  >>> dict1.popitem()
  ('square', None)
  >>> dict1.popitem()
  ('kind', 'human')
  >>> dict1
  {'width': None, 'name': 'yzw', 'length': None, 'sex': 'man', 'age': ''}

• |  setdefault(...)  不存在key，则增加到字典中，若存在，则返回key对应的value
   |      D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D

  >>> dict1.setdefault('kind','human')
  'human'
  >>> dict1
  {'kind': 'human', 'sex': 'man', 'age': '', 'name': 'yzw'}
  >>> dict1.setdefault('sex','femeal')
  'man'
  >>> dict1
  {'kind': 'human', 'sex': 'man', 'age': '18', 'name': 'yzw'}

• |  update(...)  字典合并，不能存在的k/v则增加，已存在的k则覆盖更新
   |      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]

  >>> dict1
  {'kind': 'human', 'sex': 'man', 'age': '', 'name': 'yzw'}
  >>> dict3
  {'length': None, 'width': None, 'square': None}
  >>> dict3['kind']='human'
  >>> dict3
  {'kind': 'human', 'length': None, 'width': None, 'square': None}
  >>> dict1.update(dict3)
  >>> dict1
  {'square': None, 'kind': 'human', 'width': None, 'name': 'yzw', 'length': None, 'sex': 'man', 'age': ''}
  >>> 

• |  values(...)  返回字典所有值的列表形式
   |      D.values() -> an object providing a view on D's values

  >>> dict1.values()
  dict_values([None, 'human', None, 'yzw', None, 'man', ''])

• 字典遍历

  >>> dict1
  {'width': None, 'name': 'yzw', 'length': None, 'sex': 'man', 'age': ''}
  >>> for i in dict1:
  ...     print(i,dict1[i])
  ...
  width None
  name yzw
  length None
  sex man
  age 18
  # 效率最高
  >>> for k,v in dict1.items():
  ...     print(k,v)
  ...
  width None
  name yzw
  length None
  sex man
  age 18
  #效率低
  >>> for k,v in enumerate(dict1):
  ...     print(k,v)
  ...
  0 width
  1 name
  2 length
  3 sex
  4 age
  >>> for idx,k in enumerate(dict1):
  ...     print(idx,k,dict1[k])
  ... 
  0 width None
  1 name yzw
  2 length None
  3 sex man
  4 age 18