SRD:Rod of the Python

Python: This rod is longer than normal rods. It is about 4 feet long and weighs 10 pounds. It strikes as a +1/+1 quarterstaff. If the user throws the rod to the ground (a standard action), it grows to become a giant constrictor snake by the end of the round. The python obeys all commands of the owner. (In animal form, it retains the +1 enhancement bonus on attacks and damage possessed by the rod form.) The serpent returns to rod form (a full-round action) whenever the wielder desires, or whenever it moves farther than 100 feet from the owner. If the snake form is slain, it returns to rod form and cannot be activated again for three days. A python rod only functions if the possessor is good.

Moderate transmutation; CL 10th; Craft Rod, Craft Magic Arms and Armor, baleful polymorph, creator must be good; Price 13,000 gp.