Python 字典

1. 遍历字典

• 遍历字典的键

• dict1 = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
  for key in dict1.keys():
      print(key)
  # 输出：a b c d

• 遍历字典的值

• dict1 = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
  for value in dict1.values():
      print(value)
  dict1.get('a')
  dict1.get('b')
  dict1.get('c')
  # 输出：1 2 3 4

• 遍历字典的键值对

• dict1 = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
  for k, v in dict1.items():
      print(k, ": ", v)
  # 输出：
  a :  1
  b :  2
  c :  3
  d :  4

• 更新字典

• dict1 = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
  dict2 = {'e': 5}
  dict1.update(dict2)
  print(dict1)
  # 输出：{'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5}

• 删除字典所有键值对

• dict1 = {'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5}
  dict1.clear()
  print(dict1)
  # 输出：{}

• 删除最后一个键值对

• dict1 = {'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5}
  dict1.popitem()
  print(dict1)
  # 输出：{'a': 1, 'b': 2, 'c': 3, 'd': 4}

• 比较两个字典的差异

• dict1 = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
  dict2 = {'a': 1, 'b': 2, 'c': 5, 'e': 6}
  
  differ = set(dict1.items()) ^ set(dict2.items())
  
  """输出所有的差异"""
  print(differ)
  
  # 输出:{('c', 3), ('e', 6), ('c', 5), ('d', 4)}
  
  """获取两个字典key的交集"""
  diff = dict1.keys() & dict2
  print(diff)
  
  # 输出：{'a', 'c', 'b'}
  
  """输出相同key下的不同value"""
  diff_vals = [(k, dict1[k], dict2[k]) for k in diff if dict1[k] != dict2[k]]
  print(diff_vals)
  
  # 输出：[('c', 3, 5)]

• 直接赋值何copy的区别