Step sequencer

In plain words

Each row is an instrument and each square a moment in the bar. Lit squares play, dark ones don’t. Click a square to switch it, or drag across a row to paint several at once.

class Beat(pz.App):
    pattern = ["x...x...x...x...", "....x.......x...", "x.x.x.x.x.x.x.x."]
    step = 0

    def view(self):
        return ui.audio.StepSequencer(
            pattern=self.pattern, labels=["Kick", "Snare", "Hat"], current=self.step,
            on_change=lambda e: setattr(self, "pattern", e.value),
        )

Patterns

pattern is a list of rows. Each row is either a list (True/False, or a velocity from 0 to 1 that sets how bright the step is) or text where x (or 1) is a step that plays and any other character is a rest: "x...x...x...x..." is a kick on every beat.

change gives the whole new pattern as a list of lists, ready to store. A drag starting on an empty step paints steps on; one starting on a lit step erases.

Playhead

current is the step being played: the sequencer frames that column and outlines its steps. Drive it from a timer (pz.every) or from the engine’s sequencer (node.state["step"]). Steps are shaded in groups of group (4 by default), so beats are easy to count.

Property	Default	What it does
pattern	()	Rows of steps.
labels	()	A name per row (shown on the left).
current	-1	The step being played (-1 for none).
color	"accent"	Color of the steps that play.
group	4	Steps per shaded group.
cell	22	Size of a step in pixels.

Event: on_change with the new pattern.

Tip

The drum machine demo joins a step sequencer, a row of pads and the engine’s drum module: the pads light with lit= as the steps play.