python基础入门之九 —— 推导式

 

 

 

 

一、列表推导式与普通方法对比

# 例1：while循环创建list
list0 = []
i = 0
while i < 10:
    list0.append(i)
    i += 1
print(list0)  # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# 例2：for循环创建list
list1 = []
for num in range(10):
    list1.append(num)
print(list1)  # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# 例3.1：列表推导式创建list
list2 = [i for i in range(10)]
print(list2)  # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# 例3.2：带if的列表推导式
list3 = [i for i in range(1, 10) if i % 2 == 0]
print(list3)  # [2, 4, 6, 8]

由上面可以看出：

    代码代码量：while循环>for循环>推导式

    推导式本质是for循环的化简

 

 

二、字典推导式

# 1、创建字典推导式
dict1 = {i: i**2 for i in range(1, 5)}
print(dict1)  # {1: 1, 2: 4, 3: 9, 4: 16}
# 2、字典推导式合并数列为字典
list1 = ['name', 'age']
list2 = ['Tom', 20]
dict2 = {list1[i]: list2[i] for i in range(len(list1))}
print(dict2)  # {'name': 'Tom', 'age': 20}
# 3、字典推导式提取
dict3 = {'MBP': 220, 'hp': 123, 'dell': 125}
count1 = {key: value for key, value in dict3.items() if value >= 200}
print(count1)  # {'MBP': 220}

三、集合推导式

set1 = {i**2 for i in range(3)}
print(set1)  # {0, 1, 4}
list1 = [1, 1, 2]
set2 = {i**2 for i in list1}
print(set2)  # {1, 4} 集合有去重功能