title: Numba Vectorize TypeError: 'type' object is not subscriptable
body: <p>I am trying to make my code faster by using Numba and vectorizing.
  My code is to get input from two 360 deg cameras and crop them. The main idea here is to learn how to use Numba and vectorizing. Below is my code:</p>
  
  <pre><code>import cv2
  import time
  from numba import vectorize
  import numba 
  
  dim = 1440
  
  @vectorize(['int[:, :, 3](int[:, :, 3])'], target='cuda')
  def cropFaster(img):
          croppedImG = img[:,10:1100]
          return croppedImG
  
  cap1 = cv2.VideoCapture(0)  # Set input device number
  cap1.set(3, dim)  # Set Horizontal resolution
  cap1.set(4, dim)  # Set Vertical resolution
  
  cap2 = cv2.VideoCapture(1)  # Set input device number
  cap2.set(3, dim)  # Set Horizontal resolution
  cap2.set(4, dim)  # Set Vertical resolution
  
  while (cap1.isOpened()):
          t1 = time.clock()
          ret1, img1 = cap1.read()
          ret2, img2 = cap2.read()
          croppedImgL =  cropFaster(img1) 
          croppedImgR =  cropFaster(img2)
          t2 = time.clock() - t1
          print (t2)
          cv2.imshow("Left", croppedImgL)
          cv2.imshow("Right", croppedImgR)
          if cv2.waitKey(1) &amp; 0xFF == ord('q'):
                  break 
  cap1.release()
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "transparentAPI2.py", line 9, in &lt;module&gt;
      @vectorize(['int[:, :, 3](int[:, :, 3])'], target='cuda')
    File "/usr/local/lib/python3.6/dist-packages/numba/npyufunc/decorators.py", line 120, in wrap
      vec.add(sig)
    File "/usr/local/lib/python3.6/dist-packages/numba/npyufunc/deviceufunc.py", line 391, in add
      args, return_type = sigutils.normalize_signature(sig)
    File "/usr/local/lib/python3.6/dist-packages/numba/sigutils.py", line 26, in normalize_signature
      parsed = _parse_signature_string(sig)
    File "/usr/local/lib/python3.6/dist-packages/numba/sigutils.py", line 16, in _parse_signature_string
      return eval(signature_str, {}, types.__dict__)
    File "&lt;string&gt;", line 1, in &lt;module&gt;
  TypeError: 'type' object is not subscriptable
  </code></pre>
  
  <p>Any idea how to fix this?
  Thanks</p>