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pyrung

Write ladder logic in Python. Simulate it. Test it. Deploy it.

from pyrung import Bool, PLCRunner, Program, Rung, TimeMode, out

Button = Bool("Button")
Light  = Bool("Light")

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

runner = PLCRunner(logic)
runner.set_time_mode(TimeMode.FIXED_STEP, dt=0.1)
runner.patch({"Button": True})
runner.step()

print(runner.current_state.tags["Light"])  # True

What it does

Ladder logic has always been a domain language for industrial control. pyrung asks a simple question: what if that language lived in Python?

For controls engineers: Write and simulate Click PLC logic without hardware or proprietary software. Use plain tag names from day one. Add hardware addresses when you're ready. A validator checks your program against Click constraints and tells you exactly what to fix.

For developers: VS Code becomes your PLC programming environment — step through scans, set breakpoints on rungs, watch tags update inline, and force overrides from the debug console. For the adventurous: the same program can generate a deployable CircuitPython while True scan loop for a P1AM-200 microcontroller.

How it works

Every scan is a snapshot. Logic is a pure function — the same inputs always produce the same outputs, nothing is mutated in place. Every step produces a new immutable state, so history is always there when you want it.

You drive execution. The engine never runs on its own. Call step(), run(), or run_until() from tests, a GUI, or a debugger. Pause anywhere, inject inputs, inspect any historical state.

Time is a variable. FIXED_STEP mode advances the clock by a fixed amount each scan, making timers and counters perfectly deterministic in tests. Rewind and replay whenever you need to.

Write first, validate later. Start with semantic tag names and plain Python. Map to hardware addresses when you're ready, then run the validator. It tells you what Click can and can't do — before you find out at the PLC.