pyrung

Write ladder logic in Python, test it with pytest, and deploy it to a CLICK PLC or P1AM-200.

from pyrung import Bool, PLC, Program, rung, out

Button = Bool()
Light  = Bool()

with Program() as logic:
    with rung(Button):
        out(Light)

with PLC(logic) as plc:
    Button.value = True
    plc.step()
    assert Light.value is True

Know ladder? Start with the Quickstart: a traffic light, a test, and a hardware map in ten minutes.

Know Python? Start with Know Python? Learn Ladder Logic.: eleven lessons that build a conveyor sorting station.

pip install pyrung

How it works

Every scan is a snapshot. Logic is a pure function: same inputs, same outputs, nothing mutated in place. Each plc.step() produces a new immutable state, and history keeps all of them.

You drive execution. The engine never runs on its own. plc.run_until(Motor, ~Fault) from a test, a GUI, or a debugger; pause anywhere, inject inputs, inspect any past state.

Time is a variable. PLC(logic, dt=0.010) advances the clock exactly 10 ms per scan, so a 3-second timer fires on scan 300 every time. No wall clock, no flaky tests.

What you can ask

Why a tag changed. plc.cause(Running) walks backward through scan history and names the triggers.

Why, from a dead machine. plc.why(Alarm) does the same from a tag dump alone, no recorded history needed.

How to get somewhere. plc.how(Running) finds a sequence of input changes that reaches the state, or tells you why it can't. Experimental.

Where to go

1. Install, then the Quickstart.
2. Instruction reference: every coil, timer, counter, copy, and math instruction.
3. Deploy: the CLICK quickstart maps tags to addresses and exports for ClickNick; the CircuitPython quickstart generates a P1AM-200 program.
4. Analysis: cause, effect, why, and how.