'Happy-Go-Lucky" is the kind of film that defies easy description, particularly if you're trying to persuade someone to see it.

Say it's about Poppy, a British teacher who is, well, happy all the time, and it sounds frivolous. Annoying, even.

But no. Played brilliantly by a buoyant Sally Hawkins, Poppy is a wonder. Expertly directed by Mike Leigh, "Happy-Go-Lucky" is not only joyous but substantial. Poppy doesn't ignore unhappiness in her life and in the lives of those around her. She simply navigates her way around it with an unflappable optimism.

Poppy is single, 30, lives with her friend Zoe (Alexis Zegerman) and goes out on the town with her and Poppy's younger sister, Suzy (Kate O'Flynn). Her young students love her, of course; they can spot a kindred spirit a mile away.

Her friends and family accept Poppy's happiness without understanding it. She has a series of seemingly mundane experiences that offer opportunities to darken her view of the world. None does. But to say that this is because she is in denial -- or because she simply ignores what's in front of her -- is to sell her short.

Poppy has tapped into a fundamental truth about life: Happiness is hard work.

There are opportunities to be unhappy. There is her dancing instructor (Karina Fernandez) who is near-pathological in her aggressive anger (hilariously so).

One of her students is beating up on the other kids. Poppy suspects trouble at home. A few visits from a social worker (Samuel Roukin) leads to romance.

Best of all are her weekly encounters with her driving instructor, Scott (Eddie Marsan). He is a petty tyrant who has whittled his existence down to a single purpose: to teach others how to drive. Poppy, with her attention deficits, drives him nuts.

Hawkins is marvelous. She takes what could have been a thankless, one-note role and doesn't just nail the joy, but captures the sadness that must surely lie not too far underneath. If her optimism sometimes befuddles others, it charms the audience, and makes "Happy-Go-Lucky" a singular delight.

- By Bill Goodykoontz / Gannett News Service

Happy-Go-Lucky

Rating: 3 and a half stars (out of four)

Cast: Sally Hawkins, Eddie Marsan, Alexis Zegerman.

Running time: 118 minutes.

Rated: R; language.