Drawdown-aware kill switch

mediumTradingacceptance —~20 min

Implement kill_switch(pnl, limit) — the daily loss limit as a pure function. pnl is the sequence of per-trade profits through the day, limit a positive number. Walk the cumulative profit; the moment it is at or below -limit, trading halts — and it STAYS halted for the rest of the day, even if later fills bring the total back up. Return a list of 0/1 flags, one per trade, 1 meaning halted after that trade.

This is the kill switch in this site's safety settings, reduced to twelve lines. Re-arming on a bounce is how a bad day becomes a terrible one.

example 1

input

pnl=[-100.0, -150.0, -300.0, -50.0], limit=500.0

output

[0, 0, 1, 1]

example 2

input

pnl=[-300.0, -250.0, 400.0, 100.0], limit=500.0

output

[0, 1, 1, 1]

note

The limit is hit on trade 2; the 400 win on trade 3 does not un-halt the day.

constraints

1 ≤ len(pnl) ≤ 500
limit > 0

teacher · 2 hints · the first is free

↗ read the theory

the chapter this problem is cut from

●solution.py· utf-8 · spaces:4

def kill_switch(pnl: list, limit: float) -> list:
    """1 once the day's loss limit has been hit — and stays 1."""
    total = 0.0
    out = []
    for x in pnl:
        total += x
        # TODO: once halted, stay halted — this re-arms when the total recovers
        out.append(1 if total <= -limit else 0)
    return out

ln 1, col 1tab indent · esc leave editor

python 3.13 · pyodide

+ 6 hidden on submit

input · keyword arguments to kill_switch()

pnl=[-100.0, -150.0, -300.0, -50.0], limit=500.0

expected

[0, 0, 1, 1]

the judge calls kill_switch() with exactly these inputs · outputs are compared to 6 decimal places

● standing bypython 3.13 in your browser · pyodide 0.28.3 · judged on the server to 6 dp⌘↵ run · ⌘⇧↵ submit

paper only · educational · not advice