<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _extract_mnist_images(filename, num_images):
 """Extract images from an MNIST file into a numpy array. Args: filename: The path to an MNIST images file. num_images: The number of images in the file. Returns: A numpy array of shape [number_of_images, height, width, channels]. """

  with gzip.open(filename) as bytestream:
    bytestream.read(16)
    buf = bytestream.read(_MNIST_IMAGE_SIZE * _MNIST_IMAGE_SIZE * num_images)
    data = np.frombuffer(buf, dtype=np.uint8)
    data = data.reshape(num_images, _MNIST_IMAGE_SIZE, _MNIST_IMAGE_SIZE, 1)
  return data