“I think all the Pythons are nuts in some way,” Eric Idle once wrote, “and together we make one completely insane person.” That insane entity, the comedy supergroup Monty Python, convened in 1969, with the BBC sketch show “Monty Python’s Flying Circus.” Its six members—Idle, John Cleese, Michael Palin, Terry Jones, and Graham Chapman, plus a lone American, Terry Gilliam—became the defining absurdists of postwar Britain, stomping their collective foot on polite society. You know the rest: the ex-parrot, the Comfy Chair, the Ministry of Silly Walks, the Knights Who Say “Ni!” If he had done nothing else, Idle would have given humanity an enduring gift with “Always Look on the Bright Side of Life,” the ditty that ends “Monty Python’s Life of Brian,” sung by a group of unlikely optimists while they’re being crucified. At one point, it was ranked the most played song at British funerals.