问如何解决使用Numpy时的类型错误

EN

import numpy as np
import matplotlib.pyplot as plt

def f(x):
    return x**3-2*x
def inputNumber(message):
     while True:
        try:
           userInput =float(input(message))  
        except ValueError:
           print("Enter valid")
           continue
        else:
           return userInput 
           break
 

interval1=float(inputNumber("Please write lower bound: "))
interval=float(inputNumber("Please write upper bound: "))
stepsize=float(inputNumber("Enter a step size: "))

x = np.linspace(float(interval1),float(interval),float(stepsize))
y = f(x)