from matplotlib import pyplot as plt
from skimage import data
from skimage.feature import blob_dog, blob_log, blob_doh
from math import sqrt
from skimage.color import rgb2gray
import glob
from skimage.io import imread

example_file=glob.glob(r"/home/snowbell/sample.jpg")[0]
im=imread(example_file, as_grey=True)
plt.imshow(im, cmap=cm.gray)
plt.show()

Traceback (most recent call last):
  File "test.py", line 11, in <module>
    plt.imshow(im, cmap=cm.gray)
NameError: name 'cm' is not defined