You can’t go home again, as the Americans say. It’s worth running that adage, taken from Thomas Wolfe’s unfinished novel of 1938, past those zealots who snapped up 20,000 tickets for Monty Python’s reunion at the O2 Arena in 43 seconds when they went on sale this week. Four more dates were immediately inked in, with more to follow, one feels certain, as Python fever covers the globe.