How to combine multiple images together with specified proportions in python -

how 1 go creating montage of different images, relative sizes proportional given quantity?

for instance if have:

img1=image1.png img2=image2.png img3=image3.png  render(file=img1,size=300px x 300px,file=img2,size=100px x 100px,file=img1,size=500px x 500px) 

which render image including of images 1-3 relative sizes.

any achieving appreciated!