Determine the dimensions of an image on the web without downloading it entirely

Problem
You have a list of image URLs and you want to do something with them. You need their dimensions (width, height) BUT you don’t want to download them completely.

Solution
I found a nice working solution here (see the bottom of the linked page).

I copy the code here for future references:

#!/usr/bin/env python

import urllib
import ImageFile

def getsizes(uri):
    # get file size *and* image size (None if not known)
    file = urllib.urlopen(uri)
    size = file.headers.get("content-length")
    if size: 
        size = int(size)
    p = ImageFile.Parser()
    while True:
        data = file.read(1024)
        if not data:
            break
        p.feed(data)
        if p.image:
            return size, p.image.size
            break
    file.close()
    return size, None

##########

if __name__ == "__main__":
    url = "https://upload.wikimedia.org/wikipedia/commons/1/12/Baobob_tree.jpg"
    print getsizes(url)

Sample output:

(1866490, (1164, 1738))

Where the first value is the size of the file in bytes, and the second is a tuple with width and height of the image in pixels.

Update (20140406)
I had to figure out the dimensions of some image files on my local filesystem. Here is the slightly modified version of the code above:

import ImageFile

def getsizes(fname):
    # get file size *and* image size (None if not known)
    file = open(fname)
    size = os.path.getsize(fname)
    p = ImageFile.Parser()
    while True:
        data = file.read(1024)
        if not data:
            break
        p.feed(data)
        if p.image:
            return size, p.image.size
            break
    file.close()
    return size, None

Usage:

size = getsizes(fname)[1]
if size:
    # process it