Python列表推导式

1.原始方法

list1 = []
for i in range(1, 21):
    list1.append(i)
print(list1)  # >>[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

 

2.格式1：[i for i in 可迭代的]

list0 = [i for i in range(1, 21)]
print(list0)  # >>[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

list0 = [i + 2 for i in range(1, 21)]
print(list0)  # >>[3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22]

list2 = [i for i in range(0, 20, 2)]
print(list2)  # >> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

 

3.格式2：[i for i in 可迭代的 if 条件]

 

 

 

list3 = [i for i in range(0, 20) if i % 2 == 0]
print(list3)  # >> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
print(type(list3[1]))  # >> <class 'int'>

list4 = ['89', 'hello', '2838', 'world', 'luck', '25']
list5 = [i for i in list4 if i.isalpha() == True]
print(list5)  # >> ['hello', 'world', 'luck']

4.格式3：[结果i if 条件 else 结果2 for 变量 in 可迭代对象]

 

list4 = ['89', 'hello', '2838', 'world', 'luck', 'high', '25']
list6 = [i.title() if i.startswith('h') else i.upper() for i in list4]
print(list6) # >> ['89', 'Hello', '2838', 'WORLD', 'LUCK', 'High', '25']

 

集合推导式与列表推导式相似，只是如果有相同元素则会去重

字典推导式：

dict1 = {'a': 'A', 'b': 'B', 'c': 'C', 'd': 'C'}

newdict = {value: key for key, value in dict1.items()}
print(newdict)

{'A': 'a', 'B': 'b', 'C': 'd'}