error: (-215: Assertion failed)! empty () in function 'detectMultiScale'

I'm totally lazy in linux and I'm trying to use opencv version 3.4.2 with python 3.5.2 in linux mint to run an example facial detection code. Below the code:

import numpy as np
import cv2

classificador = cv2.CascadeClassifier('\home\linux\Documentos\deteccao\haarcascade_frontalface_default.xml')

imagem = cv2.imread('pessoas.jpg')
imagemCinza = cv2.cvtColor(imagem, cv2.COLOR_BGR2GRAY)

facesDetectadas = classificador.detectMultiScale(imagemCinza, scaleFactor=1.1, minNeighbors=20, minSize=(30,30))
print(len(facesDetectadas))
print(facesDetectadas)

for (x, y, l, a) in facesDetectadas:
print(x, y, l, a)
cv2.rectangle(imagem, (x, y), (x + l, y + a), (255, 0, 255), 2)

cv2.imshow("Faces encontradas", imagem)
cv2.waitKey()

And, here below, the error:

Traceback (most recent call last):
 File "exemplo1.py", line 11, in <module>
  facesDetectadas = classificador.detectMultiScale(imagemCinza, scaleFactor=1.1, minNeighbors=20, minSize=(30,30))
cv2.error: OpenCV(3.4.2) /io/opencv/modules/objdetect/src/cascadedetect.cpp:1698: error: (-215:Assertion failed) !empty() in function 'detectMultiScale'