Yikes!
I saw this happen in the Florida everglades once. The python ate the still live gator, but he bit off more than he could chew—his stomach burst while he was trying to digest the still alive gator. Both ended up dying. Here's a similar story.
Python Bursts After Eating Gatorby Victoria Gilman
Unfortunately for a 13-foot (4-meter) Burmese python in Florida's Everglades National Park, eating the enemy seems to have caused the voracious reptile to bust a gut—literally.
Wildlife researchers with the South Florida Natural Resources Center found the dead, headless python in October 2005 after it apparently tried to digest a 6-foot-long (2-meter-long) American alligator. The mostly intact dead gator was found sticking out of a hole in the midsection of the python, and wads of gator skin were found in the snake's gastrointestinal tract.
The gruesome discovery suggests that the python's feisty last meal might have been simply too much for it to handle...
http://news.nationalgeographic.com/news/2005/10/1006_051006_pythoneatsgator.html