typeerror:只有length-1数组可以转换为python scalars python array和numpy

这是我的密码但我有上述错误。我以前找过,但没帮我找到答案这段代码中有什么不正确?

import numpy as np 
import math

def sigmoid(x):
    s = np.array(None)
    for i in x:
        np.append(s,(1/(math.exp(-x)+1)))

    return s

x = np.array([1, 2, 3])
sigmoid(x)

<ipython-input-31-8e002c20e792> in sigmoid(x)
     17     s = np.array(None)`
     18     for i in x:
---> 19         np.append(s,(1/(math.exp(-x)+1)))
     20     return s
TypeError: only length-1 arrays can be converted to Python scalars