Venins (1991)

Marc, a young snake expert, works at a museum in Geneva. He loves snakes, to the point that he owns many and even takes a bath with his huge pet python. He meets and falls in love with a beautiful young woman named Malenka, who is the assistant--and mistress--of an older herpetologist professor. Marc discovers that not only is the "professor" a fraud but also a dangerous psychotic who had at one time seduced Marc's mother, and Marc believes that the longer Malenka stays with him, the greater danger she's in.