Based on a play, probably some variation as screenplays go, but it just gets funnier. From a technical process point of view, it was shot on 35mm for the Deluxe Color process, which eventually beat out the superior but complex Technicolor process.
Cool as a rom-com and set in the UK and Paris with mostly interior sets.
Worth watching for historical value in fashion and design.
The play itself seems to be hard to track down, the novel of the movie itself also could be hard to find.
Just watch the move.