Opencv polylines function in python throws exception

This function is not enough well documented and the error are also not very useful. In any case, cv2.polylines expects a list of points, just change your line to this:

import cv2
import numpy as np

img = np.zeros((768, 1024, 3), dtype='uint8')

points = np.array([[910, 641], [206, 632], [696, 488], [458, 485]])
cv2.polylines(img, [points], 1, (255,255,255))

winname = 'example'
cv2.namedWindow(winname)
cv2.imshow(winname, img)
cv2.waitKey()
cv2.destroyWindow(winname)

The example above will print the following image (rescaled):

The problem in my case was that numpy.array created int64-bit numbers by default. So I had to explicitly convert it to int32:

points = np.array([[910, 641], [206, 632], [696, 488], [458, 485]])
# points.dtype => 'int64'
cv2.polylines(img, np.int32([points]), 1, (255,255,255))

(Looks like a bug in cv2 python binding, it should've verified dtype)