In truth, Rachel Weisz was “just being rather stubborn.”

She had just spent months in the darkest depths of drama, shooting “The Constant Gardener” and “The Fountain.” It was time, she declared, for a comedy.

“Which was kind of exactly what I wasn’t being offered,” the 38-year-old actress recalls. Then she got her hands on a strange script called “The Brothers Bloom,” a con-man comedy that seemed equal parts whimsy and gunpowder.

“When I read this one, I thought, ‘Oh, yeah, this is the role, this is the one,’” she says on the phone from her home in New York a week before the film’s release.

But there was a problem: The movie “was not, I believe, something the director and producer were considering me for,” she explains.

No matter. Weisz, who won an Oscar for her role in “The Constant Gardener,” was already consumed with the notion of playing Penelope Stamp, a reclusive heiress who spends all of her time acquiring new hobbies.

“It’s great writing. It’s very unusual, very interesting, very funny,” she says of the film, in which she stars opposite Adrien Brody and Mark Ruffalo. “It coincided with my tastes and sense of humor – not that I’d ever read anything like it. And, yeah, I fell in love with the character.”

It was up to Weisz to convince writer-director Rian Johnson that the British-born beauty could pull off the comedic, eccentric role. “I was just completely direct that I really, really wanted to play the role,” she recalls. “And that I’d work very hard and try and do a good job.”

Her entreaties worked. She got the gig, but then there was the small matter of figuring out how to portray this idiosyncratic young woman. “There wasn’t any actual preparation I could do in terms of research to play an unsocialized heiress. … If they exist, none of them came forward to meet me,” Weisz says. “So it was just an active imagination. I was just trying to imagine someone who’d never been out much, never had friends or dated people, but just had been focusing on her hobbies.”

For the hobbies, Weisz had no choice but to prepare. Within the first half-hour of the film, her character plays the harp, the piano, the accordion and the banjo. She juggles and plays table tennis, does gymnastics and karate, creates pinhole cameras and crafts origami birds. She crashes one fancy car after another, rides a unicycle and a skateboard and even tries to rap.

“That was so embarrassing because I had to rap to Brody, who is from Queens – I mean he’s really into hip-hop – and I’m from North London. I just had no sense of how it should sound,” she says. “Brody was looking at me like the Earth was going to swallow him up with shame that I was dissing his culture.”

To capture the drama of a swindle that brings Penelope and the brothers Bloom around the world, the film was shot in locations across Eastern Europe. “We were on the road from Serbia to Montenegro to Croatia to Prague to Romania,” Weisz says. “It was like being in a traveling circus – a little more luxurious, but not much.”

Despite the lack of luxury, the process of making a comedy was exactly what the actress had hoped for.

“It was tremendously satisfying. I think it’s harder than drama in many ways,” she says, “because even though they’re bizarre people, they’re not two-dimensional characters. So we had to keep them flesh and blood, but while saying things outside the norm of naturalism.”

Having gotten her comedy fix with “The Brothers Bloom,” Weisz was again ready to immerse herself in serious dramas. Last month she was at the Cannes Film Festival with the premier of “Agora,” a historical love story about a female philosopher set in 4th-century Roman Egypt. She also recently filmed an adaptation of Alice Sebold’s novel “The Lovely Bones,” about a young girl who has been murdered and looks down at her grieving family from heaven. That film, in which she plays the girl’s mother, is expected to be released in December.

And this summer, Weisz returns to the stage for the first time in eight years. She had been wanting to do a play for a while, and not too long ago the Donmar Warehouse, a theater in London’s West End, approached her with an offer to star in a little show called “A Streetcar Named Desire.”

“I was just waiting for the role that really got me fired up, and I’ve actually never seen ‘Streetcar,’” she says. “So when I read it, it was really for the first time – and if there’s a better role written for a woman, I haven’t come across it.”

Especially a woman who has now proven her skill at drama – and comedy.