Clearly a cussing cousin of Broadway Danny Rose, Emmet Ray is a classic Woody Allen creation, writes David Parkinson.

Living in the shadow of his idol, Django Reinhardt, he has to settle for being the second greatest jazz guitarist of the thirties, while retaining all the attitudes and delusions that go with being top of the pile.

It takes an actor with a supreme comic touch to prevent such a feckless, self-obsessed rogue from becoming a loathsome monster and it may come as a surprise to learn that in Sweet and Lowdown Sean Penn is just the man for the job.

Learning the fretwork for all the songs is one thing, but transforming himself into a droning egocentric, who's a demon under the influence and an angel on stage, and still be funny with it, ranks as one of the finest achievements of Penn's impressively varied career. Nothing typifies the blend of pomposity and buffoonery better than the silent slapstick sequence in which Emmet descends to the stage perched precariously on the cusp of a crescent moon. It sums up both the era and the character to perfection.

Equally deserving of her Oscar nomination (although neither won) is Samantha Morton, who borrows the gestures and grimaces of Harpo Marx to fashion a display of heartbreaking innocence as Hattie, the mute laundress who becomes Emmet's unlikely lover. Delighting in his favourite pastimes of watching trains go by and shooting rats at the city dump, she has an aura of optimistic trust that eventually lands her a role in a silent movie. His prattling and her mime give the film its soul and the pace and mood alters deleteriously during her prolonged absence. This is because Emmet has taken up with Blanche, a slumming socialite whose habit of toying with the lower orders brings him into contact with the Mob.

Played with statuesque insouciance by Uma Thurman, Blanche is Marlene Dietrich trapped in an F. Scott Fitzgerald novel and yet she can't make us forget Hattie. However, this episode does provide the film with one of its highlights.

Told as a series of vignettes, Sweet and Lowdown is a fond tribute not just to the jazz age, but also to the way a mythology has grown up around the music that plays like a free-form variation each time it's related. This tendency to embroider is hilariously captured in the Rashomon-like staging of the gas station incident, in which three different versions of the tale are presented as gospel truth. Photographed with an evocatively shabby nostalgia by Fei Zhao (who is best known for such Chinese masterpieces as Raise the Red Lantern) and laced with Allen's customary flashes of wit, this may only be a mood piece in a minor key. But it still provides a musical education and a masterclass in character submersion.