无法转换 Python 列表中项目的值或类型

Question

为什么不能更改列表项的类型或值？a = ['3.465759','2.8797','9.23544']for each in a:    print(each)    each = round(float(each),3) + 2    print(a)结果是   ['3.465759', 2.8797, '9.23544']

Answer 1

eacha是在下一次迭代中取下一个值的循环变量。将转换后的值存储在另一个列表中。

a = ['3.465759','2.8797','9.23544']

b = []

for each in a:

    print(each)

    each = round(float(each),3) + 2    

    b.append(each)

print(b)

输出：

3.465759

2.8797

9.23544

[5.466, 4.88, 11.235]

或者

如果你想就地修改列表，那么

a = ['3.465759','2.8797','9.23544']

for i in range(len(a)):

    each = a[i]

    print(each)

    each = round(float(each),3) + 2

    a[i] = each

print(a)

或者

使用列表理解

[round(float(each),3) + 2 for each in a]

Answer 2

您可以使用地图：

a = ['3.465759','2.8797','9.23544']
float_list = list(map(float, a))
print(float_list)

输出：

[3.465759, 2.8797, 9.23544]

Answer 3

a = ['3.465759','2.8797','9.23544']

result = []

for each in a:

    each = round(float(each),3) + 2  

    result.append(each)

print(result)

Output: [5.466, 4.88, 11.235]

这是你想要的？

Answer 4

你没有改变a，当你进行转换时，请确保更改值：即：

a = ['3.465759','2.8797','9.23544']

for i  in range(len(a)):

    each = a[i]

    print(each)

    each = round(float(each),3) + 2 

    a[i] = each   

print(a)

或者

a = ['3.465759','2.8797','9.23544']

for i, each in enumerate(a):

    print(each)

    each = round(float(each),3) + 2 

    a[i] = each   

print(a)

3.465759

2.8797

9.23544

[5.466, 4.88, 11.235]