PIL: How to make area transparent in PNG?

Question

I've been using PIL to crop Images, now I also want to make certain rectangular areas transparent, say

from PIL import Image
im = Image.open("sample.png")
transparent_area = (50,80,100,200)
...

Answer 1

from PIL import Image
from PIL import ImageDraw
im = Image.open("image.png")
transparent_area = (50,80,100,200)

mask=Image.new('L', im.size, color=255)
draw=ImageDraw.Draw(mask) 
draw.rectangle(transparent_area, fill=0)
im.putalpha(mask)
im.save('/tmp/output.png')

I learned how to do this here.