How to zero pad a PIL Image?

I want to add zeros on all sides of image. I try:

from PIL import Image
im = Image.open("/content/drive/My Drive/image31.png")

def pad(im,layers):
    return [[0]*(len(im[0])+2*layers)]*layers    + \
           [[0]*layers+r+[0]*layers for r in im] + \
           [[0]*(len(im[0])+2*layers)]*layers
pad(im,1)

Error is : TypeError: 'PngImageFile' object does not support indexing