python基础——推导式

列表推导式

又名列表生成式

建立列表的几种方法

# 1. 准备一个空列表
list1 = []
# 2. 书写循环，依次追加数字到空列表list1中
i = 0
while i < 10:
    list1.append(i)
    i += 1
print(list1)
# ---------------------------------
list2 = []
for i in range(10):
    list2.append(i)
print(list2)
# ---------------------------------
list3 = [i for i in range(10)]
print(list3)
 
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

高级用法

list1 = [i for i in range(10) if i % 2 == 0]
print(list1)
 
list1 = [(i, j) for i in range(1, 3) for j in range(3)]
print(list1)
 
# [0, 2, 4, 6, 8]
# [(1, 0), (1, 1), (1, 2), (2, 0), (2, 1), (2, 2)]

字典推导式

# {key: value for循环 if判断}
dict1 = {i: i**2 for i in range(1, 5)}
print(dict1) # {1: 1, 2: 4, 3: 9, 4: 16}
 
list1 = ['name', 'age', 'gender']
list2 = ['Tom', 20, 'man']
dict1 = {list1[i]: list2[i] for i in range(len(list1))}
print(dict1) # {'name': 'Tom', 'age': 20, 'gender': 'man'}
 
counts = {'MBP': 268, 'HP': 125, 'DELL': 201, 'Lenovo': 199, 'acer': 99}
# 需求：提取上述电脑数量大于等于200的字典数据
count1 = {key: value for key, value in counts.items() if value >= 200}
print(count1) # {'MBP': 268, 'DELL': 201}

集合推导式

list1 = [1, 1, 2]
set1 = {i ** 2 for i in list1}
print(set1) # {1, 4}