Do you know people in real life who are relentlessly perky and chattery, oblivious to the legitimate dangers in the world, and unable to take anything seriously? Of course you do. And do those people drive you crazy? Of course they do.

What’s remarkable about Mike Leigh’s “Happy-Go-Lucky” is that while the main character is exactly that sort of person, she doesn’t irritate me. She is charming and funny, and her blithe, carefree spirit actually comes across as a legitimate way of dealing with life — or, at the very least, as being better than some of the alternatives.

What’s also remarkable is that Mike Leigh’s last two films were very dreary: “Vera Drake,” about a kindly abortionist, and “All or Nothing,” about a lot of very unhappy British people. Poppy, the ebullient ninny at the center of “Happy-Go-Lucky,” would be unable to watch more than five minutes of those movies. Leigh following “Vera Drake” with “Happy-Go-Lucky” is like Martin Scorsese following “Raging Bull” with a Spongebob cartoon.

Poppy, played to utter perfection by Sally Hawkins, sums up her attitude in the first dialogue of the film, when she enters a bookstore, sees a volume called “The Road to Reality,” and says with a laugh, “Oh, I don’t want to be going there!” When she exits the store, she finds her bicycle has been stolen and laments, “I didn’t even get a chance to say goodbye!” Over and over again you will see things happen that ought to irritate or anger or sadden Poppy, and yet she refuses to be irritated or angered or saddened. She makes Pollyanna look like Sylvia Plath.

She’s a perfect fit for her job — she teaches elementary school — and her best friend and flatmate, Zoe (Alexis Zegerman), a fellow teacher, gets along with her just fine. Not everyone is as tolerant of Poppy’s incessantly chipper demeanor, however, and Poppy is chatty with everyone, including (especially?) those who don’t want to chat.

There isn’t much of a plot in the film, which was written by Leigh and has a lot of improvisational dialogue. It’s simply a character study, an exquisitely detailed snapshot of Poppy’s life. With her bike gone, she finally learns to drive, with a surly instructor named Scott (Eddie Marsan) as her guide. She takes a flamenco-dancing class with a co-worker. She deals with a problematic student. She goes to the chiropractor for back problems, and laughs when she feels pain. We frequently see people whose anger gets the best of them, lending credence to the argument that Poppy’s head-in-the-sand philosophy might be better. It’s better for one’s blood pressure, that’s for sure.

The movie is occasionally laugh-out-loud funny, but it’s generally just whimsical and upbeat. And Hawkins’ performance is nothing short of mesmerizing: How can this woman exist? She is such an exaggeration, yet she seems so believable. Someone tells her, “You can’t make everyone happy,” and she responds, “There’s no harm in trying, though, is there?” Well, except that you annoy people who don’t want to have your sunshine shoved down their throats. But on general principle, yes, there’s no harm in doing your best to spread happiness around.

Is Poppy naive and oblivious? Does she intentionally ignore bad situations, or does she truly not see them? She’s certainly not unintelligent. Her character arc is unusual in that while most movie protagonists are somehow different at the end from what they were in the beginning (they’ve learned something, they’ve endured something, etc.), Poppy doesn’t change — and that’s her arc. The message is that she’s NOT going to change. This is who she is, and she’s happy with herself. Whether that’s good or bad is a topic for a post-movie discussion on Poppy herself and the other Poppys of the world.

B+ (1 hr., 58 min.; R, some vulgarity and profanity, one scene with a flurry of F-words .)