It’s easy to lazily assume that most biographical films about writers – this one’s about a year in the life of Roald Dahl – are safe and boring and uncinematic, composed of endless shots of the subject perched over their typewriter or laptop while waiting for inspiration to strike before suddenly hitting the keys in a mad rush of genius.

John Hay To Olivia

A predictable yawn, in other words. But not automatically. Not all of them, at least. Think of An Angel at My Table, Iris, Shakespeare in Love, Midnight in Parisand Colette. Or the weirdly hallucinogenic part-biography, part-novel that is Naked Lunch. Or Barton Fink, which is fictional though based on the playwright Clifford Odets. Films about well-known authors, when you look more closely, are as varied as the literature these writers are known for. And there’s no shortage of≈imagination and cinematic risk-taking in that list.

This new film about the British children’s author Dahl restricts itself to a year in the lives of the author and his wife, the...