Snake catcher Luke Dunn was called by Old Parliament House security to retrieve the non-venomous python, which isn't native to the ACT, at around 11pm on Sunday night. Mr Dunn handed the snake to ACT Parks and Conservation on Monday morning.

The python was assessed by a government vet on Monday and showed signs of malnutrition, parasite infestation and old injuries.

"The snake had to be euthanised for welfare reasons," ACT Parks and Conservation said.

Mr Dunn said it was likely the python caught a ride on a vehicle into the ACT or it was an escaped pet. Carpet pythons were found along the east and northern coast of Australia and in inland locations, he said.

"They're easy to look after and get to a good size for people to handle," Mr Dunn said.

But Mr Dunn was uncertain the python found on Sunday was a pet. "It was very lean, very, very strong. It also had parasites along its skin. It had mites on it," he said, which pointed to the snake being wild.

Snakes exotic to Australia are euthanised but carpet pythons, which are native to parts of Australia, would generally be released or returned, Mr Dunn said.

Snakes could go to a zoo or another person who presents snake displays, he said.

"It really depends on what the vet says."

An ACT Parks and Conservation spokesman said every effort was made to rehabilitate and rehome surrendered native pythons.

"We remind owners to never release a captive-bred python into the wild."

Mr Dunn said it was the first call out to retrieve a snake in the Parliamentary Triangle he had received.

"There's not much there for snakes," he said.

It wasn't the only snake caught in Canberra at the weekend. An extremely venomous eastern brown snake was caught on Bunda Street in Civic on Sunday. It was released at an undisclosed location away from houses.