Minimal reactive state for Python.

• Small core. No runtime dependencies.
• Signal-first model. State, derived state, and effects form the primitive graph.
• Structural typing. Internal contracts use Protocol, not inheritance.
• Python 3.13 generics. State[T] and Computed[T] use PEP 695 syntax.
• Dynamic dependencies. Effects replace their dependency set on each run.
• Equality short-circuit. Unchanged values do not notify dependents.

from st import State, computed, effect, peek

count = State(1)
double = computed(lambda: count.value * 2)

effect(lambda: print(double.value))

count.value = 2

current = peek(double)

Output:

2
4

Core infrastructure:

• dispose
• untrack
• peek (done)
• batch
• on_cleanup

Scheduling:

• custom effect schedulers
• queued flush
• next_tick

Debugging:

• runtime type guards
• dependency inspection
• subscriber inspection
• optional labels

uv sync
uv run pytest