Python erro em código python e bibliotecas dlib e opencv

[mike.ferro]

boas pessoal

estou a trabalhar em python com as bibliotecas dlib e opencv e quero excutar um codigo simples mas aparece-me um erro, o codigo é o seguinte: 

# import the necessary packages

from imutils import face_utils

import dlib

import cv2



# initialize dlib's face detector (HOG-based) and then create

# the facial landmark predictor

p = "shape_predictor_68_face_landmarks.dat"

detector = dlib.get_frontal_face_detector()

predictor = dlib.shape_predictor(p)



# load the input image and convert it to grayscale

image = cv2.imread("example.jpg")

gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)



# detect faces in the grayscale image

rects = detector(gray, 0)



# loop over the face detections

for (i, rect) in enumerate(rects):

# determine the facial landmarks for the face region, then

# convert the facial landmark (x, y)-coordinates to a NumPy

# array

shape = predictor(gray, rect)

shape = face_utils.shape_to_np(shape)



# loop over the (x, y)-coordinates for the facial landmarks

# and draw them on the image

for (x, y) in shape:

cv2.circle(image, (x, y), 2, (0, 255, 0), -1)



# show the output image with the face detections + facial landmarks

cv2.imshow("Output", image)

cv2.waitKey(0)

 

e da-me erro quando introduzi

predictor = dlib.shape_predictor(p)

aparece

Unable to open shape_predictor_68_face_landmarks.dat

alguém me pode ajudar??