TypeError : 내가하지 않았음에도 불구하고 'numpy.float64'유형의 비 정수로 시퀀스를 곱할 수 없습니다.

이 코드는 함수로 만들기 전에 잘 작동했습니다. 그런데 무엇이 잘못 되었나요? 코드의 어느 곳에서나 문자열 / 목록을 부동 숫자로 곱한 것을 볼 수 없습니다.

import matplotlib.pyplot as plt
from scipy.optimize import curve_fit
import numpy as np
from numpy import * #This is temporary

def NonlinearReg(xdata,ydata,f):
    Constants, Covariance = curve_fit(f, xdata, ydata)
    return Constants

def Nonlinear_Plot(xdata,ydata,f,a,b,c):
    plt.figure(figsize=(6, 4))
    plt.scatter(xdata, ydata, label='Data')
    plt.plot(xdata, f(xdata, a, b, c), label='Best Fit')
    plt.legend(loc='best')
    plt.show()

def main():
    xdata = [2,8,6,7]
    ydata = [9,6,5,4]
    NonlinearFunction = input("Type in the Nonlinear Function : \n")
    ff= lambda x,a,b,c: eval(NonlinearFunction)
    a,b,c=NonlinearReg(xdata,ydata,ff)
    if (c==1): #The initial guess is as it is; the given function doesn't involve in c
        print('\n', '[a b] for the best fit= ', '['+str(a) +'   '+str(b)+ ']' ,'\n')
    else:
        print('\n', '[a b c] for the best fit= ', '['+str(a) +'   '+str(b)+'   '+str(c)+ ']' ,'\n')

    Nonlinear_Plot(xdata, ydata,ff, a,b,c)

main()

'a + b * x'와 같은 입력 함수로 이것을 실행하면 다음과 같은 결과를 얻을 수 있습니다 (Visual Studio 2019에서 실행).

Type in the Nonlinear Function :
a+b*x
C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python37_64\lib\site-packages\scipy\optimize\minpack.py:808: OptimizeWarning: Covariance of the parameters could not be estimated #How can I stop this error from coming up?
  category=OptimizeWarning)

 [a b] for the best fit=  [9.879518072308521  -0.6746987951843755] #it does provide the constants a,b

Traceback (most recent call last):
  File "C:\Users\Essam\source\repos\PythonApplication2\PythonApplication2\PythonApplication2.py", line 44, in <module>
    main()
  File "C:\Users\Essam\source\repos\PythonApplication2\PythonApplication2\PythonApplication2.py", line 42, in main
    Nonlinear_Plot(xdata, ydata,ff, a,b,c)
  File "C:\Users\Essam\source\repos\PythonApplication2\PythonApplication2\PythonApplication2.py", line 13, in Nonlinear_Plot
    plt.plot(xdata, f(xdata, a, b, c), label='Best Fit')
  File "C:\Users\Essam\source\repos\PythonApplication2\PythonApplication2\PythonApplication2.py", line 34, in <lambda>
    ff= lambda x,a,b,c: eval(NonlinearFunction)
  File "<string>", line 1, in <module>
TypeError: can't multiply sequence by non-int of type 'numpy.float64'

코드는 함수로 만들기 전에 실행되었습니다.

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

def func(x, a, b,c): 
    return ff(x,a,b,c) 

ff= lambda x,a,b,c: eval("a*x**b")

xdata = [0 ,866, 2753, 4763, 6942, 10593]
ydata = [30, 23, 27, 26, 23, 20]

popt, pcov = curve_fit(func, xdata, ydata)
print('\n', '[a b] for agmad fitting =    ', popt,'\n')

plt.figure(figsize=(6, 4))
plt.scatter(xdata, ydata, label='Data')
plt.plot(xdata, ff(xdata, popt[0], popt[1], popt[2]), label='Agmad Fit')
plt.legend(loc='best')
plt.show()