I am searching for a film from 70's or 80's about a scientist who is attempting to create a snake (cobra?) from a human by injecting small quantities of venom. I can remember some of the details - there was a circus with a freak show. In it was "snakeman" half human half snake. This was one of the scientist's early attempts that went wrong. Also, the scientist's beloved python was killed by a gang and he got his own back by throwing a black mamba into the shower cubicle of the gang leader. Film ended with the human turning into a snake and biting the scientist! Sounds corny and probable a rubbish film but I am curious...