如何在Python中创建字典

字典是Python中的基本数据结构，对Python程序员来说非常重要。它们是数据值的无序集合，用于像地图一样存储数据值。字典是可变的，这意味着它们可以更改。它们提供O(1)的时间复杂度，并针对内存开销和查找速度效率进行了大量优化。

示例 1：每个子列表的第一个元素是键，第二个元素是值。我们希望动态存储键值对。

# Python program to demonstrate
# dynamic dictionary creation
  
  
# Initialize an empty dictionary
D = {} 
  
L = [['a', 1], ['b', 2], ['a', 3], ['c', 4]]
  
# Loop to add key-value pair
# to dictionary
for i in range(len(L)):
    # If the key is already 
    # present in dictionary
    # then append the value 
    # to the list of values
    if L[i][0] in D:
        D[L[i][0]].append(L[i][1])
      
    # If the key is not present
    # in the dictionary then add
    # the key-value pair
    else:
        D[L[i][0]]= []
        D[L[i][0]].append(L[i][1])
          
print(D) 

输出：

{'a': [1, 3], 'b': [2], 'c': [4]}

示例 2：

# Python program to demonstrate
# dynamic dictionary creation
  
  
# Key to be added
key_ref = 'More Nested Things'
my_dict = {
    'Nested Things': [{'name', 'thing one'}, {'name', 'thing two'}]
}
  
# Value to be added
my_list_of_things = [{'name', 'thing three'}, {'name', 'thing four'}]
  
# try-except to take care of errors
# while adding key-value pair
try:
    my_dict[key_ref].append(my_list_of_things)
      
except KeyError:
    my_dict = {**my_dict, **{key_ref: my_list_of_things}}
      
print(my_dict)

输出：

{
 'Nested Things': [{'name', 'thing one'}, {'thing two', 'name'}], 
 'More Nested Things': [{'name', 'thing three'}, {'thing four', 'name'}]
}