Python 类型错误 : can't multiply sequence by non-int of type 'float'

Question

我有这个代码

a = [0.0, 1.1, 2.2]
b = a * 2.0

这就是我得到错误的地方

typeError: can't multiply sequence by non-int of type 'float'

我希望它返回的是

b = [0.0, 2.2, 4.4]

Answer 1

错误是您将一个列表(即 a)和一个 float (即 2.0)相乘。

改为这样做(列表理解)

b = [i*2.0 for i in a]

一个小演示

>>> a = [0.0, 1.1, 2.2]
>>> b = [i*2.0 for i in a]
>>> b
[0.0, 2.2, 4.4]

使用 map

map(lambda x:x*2.0 , a)

这是 timeit 结果

bhargav@bhargav:~$ python -m timeit "a = [0.0, 1.1, 2.2]; b = [i*2.0 for i in a]"
1000000 loops, best of 3: 0.34 usec per loop
bhargav@bhargav:~$ python -m timeit "a = [0.0, 1.1, 2.2]; b = map(lambda x:x*2.0 , a)"
1000000 loops, best of 3: 0.686 usec per loop
bhargav@bhargav:~$ python -m timeit "import numpy; a = numpy.array([0.0, 1.1, 2.2]); b = a * 2.0"
10 loops, best of 3: 5.51 usec per loop

列表理解是最快的。