如何用 Python 创建字典
字典 是 Python 中的基础数据结构,对于 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,这意味着它们可以改变。它们的时间复杂度为O(1)
,并且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]}
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'}]
}
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