function()接受4个位置参数,但在Python 3.5中为5个提供了_def函数

我试图从我的数据中拟合指数函数。我对将数学函数拟合到我的数据还不是很有经验。 下面是我现在的代码。

import numpy as np
import matplotlib.pyplot as plt
from scipy.optimize import curve_fit

my_x = (4,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40)
my_y = (0.022172333,0.020881,0.017729,0.021641333,0.02479,0.030755667,0.037235,0.048389,0.068451,0.06898974,0.161409,0.242802333,0.316012667,0.440762333,0.569118333,0.7016839,0.832527333)

def myfunc(x,a,b,c):
    return a*np.exp(b*x)+c


p=[my_x,0.0045,0.1262,0] #pre-determined a=0.0045, b=0.1262, c=0 according to excel
popt, pcov = curve_fit(myfunc,my_x,my_y, p0=p)


plt.plot (my_x,myfunc(my_x, *popt))

我得到的错误消息如下。

return function(xdata, *params) - ydata

TypeError: myfunc() takes 4 positional arguments but 5 were given

我不太明白这个错误消息在说什么。谁能帮我理解是什么导致了这个错误,以及我如何改进代码?