这是我在python中的代码：

import numpy as np
import cv2

face_cascade = cv2.Cascadeclassifier('haarcascade_frontalface_default.xml')
eye_cascade = cv2.Cascadeclassifier('haarcascade_eye.xml')

img = cv2.imread('human.png')
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

faces = face_cascade.detectMultiScale(gray,1.3,5)
for (x,y,w,h) in faces:
    img = cv2.rectangle(img,(x,y),(x+w,y+h),(255,0),2)
    roi_gray = gray[y:y+h,x:x+w]
    roi_color = img[y:y+h,x:x+w]
    eyes = eye_cascade.detectMultiScale(roi_gray)
    for (ex,ey,ew,eh) in eyes:
        cv2.rectangle(roi_color,(ex,ey),(ex+ew,ey+eh),(0,255,2)

cv2.imshow('img',img)
cv2.waitKey(0)
cv2.destroyAllWindows()

这是错误：

Traceback (most recent call last): 
File "image.py",line 10,in faces = face_cascade.detectMultiScale(gray,5)  
cv2.error: OpenCV(4.1.2) /io/opencv/modules/objdetect/src/cascadedetect.cpp:1689: 
error: (-215:Assertion failed) !empty() in function 'detectMultiScale'

enter image description here