Isabelle Huppert, lost in character, sits at a traffic light and giddily sings along with the radio, earning giggles from the biker who pulls up next to her.

Patience is her name, and she’s having a good day. Or maybe it’s what comprises that “good day” that lightened her mood, just by its scent.

There’s all this hashish packed up in the hatchback, stuffed to the roof. The retired police drug-sniffing dog she rescued helped her find it. And Patience, high or just high on the possibilities, is beside herself.

She’s got a mother in a very pricey Paris nursing home, high association fees at her apartment, her late husband’s debts to settle — lots of “expenses.” But she’s got this hashish and she’s got an angle.

The daughter of an Algerian father and Holocaust survivor mother, she’s fluent in Arabic. She translates for the police drug interdiction squad. Any phone conversation, in Arabic, with the folks who brought in the hash or are planning to distribute it — now through her — she will hear. She knows who to sell the hash to. And the suspect the cops come to know as “La Matron,” aka “Mama Weed,” will only be passing on to the police what she wants them to hear.

Oh, and the chief of that squad (Hippolyte Girardot)? He’s her boss….with benefits.

“Mama Weed” is a cackle-out-loud drug smuggling thriller, a suspenseful, cynical and often very amusing comedy about somebody with “an existential” problem with what she does for a living, who finds it also creates opportunities for her, opportunities fraught with risk but which she leaps into because of who she is and where her loyalties lie.

We get a hint that Patience, back in the day, drove a family boat on “runs” into Switzerland. Dad was sketchy, and he raised a daughter indifferent to let’s just say “the law.” Her probably-sketchy husband died decades ago with a lot of tax debts.

She’s behind on her payments at the private care nursing home when a conversation she’s wiretapped into gives her a start. This smuggler the cops are digitally tracking, hoping for a big score, is on the phone with the kindly nurse, Kadidja (Farida Ouchani) who cares for Patience’s mother.

There’s nothing for it but to mistranslate and mislead the police, get in a taxi and run over to warn her. In an instant, she’s committed to saving the woman’s son because of “all you’ve done for my mother.”

And with that, we’re off to the races as our anti-heroine puzzles over how to fool her bosses, trick and foil the scary drug gang, invent a new identity — looking up how to disguise herself in a hijab online — and make a lot of money in a very short period of time.

Can she pull it off?

Director and co-writer Jean-Paul Salomé (“The Chameleon,” “Girls with Guns”) has engineered a clever, comical script built on coincidences and quirky, unconventional relationships.

Patience “knows” the “small fry” drug smugglers she helped identify “Scotch” (Rachid Guellaz) and “Cocoa Puff” (Mourad Boudaoud). She’s got their damned phone numbers, for Pete’s sake. A burner phone, a text message in Arabic, and she’s in business.

A clever touch — one big time dealer has figured out that the most private chat space of all, the one the cops never get wise to, is communicating in the middle of online first-person shooter video games. Log in, get into a shootout, shout out your conversation to your foe.

Cute twists also include the amusing places Patience selects for the hand-offs, and the small world of petty (and not so petty) corruption she wades into, crossing paths with assorted relatives of her working class Chinese immigrant landlady (Nadja Nguyen).

The music and the pace of the editing raise the stakes and up the tempo in the later acts. This flippant, fun movie skips by at a brisk-never-rushed quick canter.

But its the laugh-out-loud chutzpah of it all and Huppert’s cocksure, casual and lie-on-the-fly amorality in the title role that gives “Mama Weed” her buzz. Huppert has never been sunnier or funnier.

MPA Rating: unrated, violence, drug content, profanity

Cast: Isabelle Huppert, Hippolyte Girardot, Rachid Guellaz, Farida Ouchani and Nadja Nguyen

Credits: Directed by Jean-Paul Salomé, script by Jean-Paul Salomé, Hannelore Cayre. A Music Box release.

Running time: 1:45