How to update source code without rebuilding image

Hi guys, i’m using Docker toolbox for win7
Basically , i built an docker image for my python project and push it to dockerhub and everything works fine.
But now i need to change some code in my python source code ( The dockerfile still the same , i just change the python source code).
Is there anyway to fast update it to the docker images and update to dockerhub because building a new image takes like forever.
Thanks