PiercingLine — Piercing Line

A white bar that opens below the previous black bar’s low and closes back above the midpoint of its body: the gap down was rejected and then some. Returns +1.

Signature

PiercingLine(lookback, on=<source>)

Argument	Type	Required	Notes
lookback	int Param	Yes	Pinned at 1; the recogniser keeps the previous bar in state. Bounds 1–1.
on=	symbol	No	Source symbol. Defaults to the trade symbol. Reads open, high, low, close.

Formula

Prior bar black; this bar opens below its low and closes above the midpoint of its body but below its open.

Warmup

One bar of state.

Reading the value

p.value
p > 0

Pattern indicators return a flag, not a level: +1 bullish, -1 bearish, 0 absent. They are zero on most bars by design, so treat them as event triggers rather than as something to smooth or cross.

Example

class PiercingEntry(Strategy):
    """Act on the pattern only in the direction of the longer trend."""
    trade = Symbol()
    sizing = FixedCapital()

    def execute(self):
        p = PiercingLine(1, on=self.trade)
        sma = SMA(50, on=self.trade)
        if p.value > 0 and self.trade.is_flat:
            self.buy(self.trade, reason="Piercing line")
        if self.trade.is_long and self.trade.close < sma.value:
            self.sell(self.trade, self.trade.position, reason="Trend lost")

Notes

• The bullish mirror of DarkCloudCover. Requires a genuine gap below the prior low, which makes it rare on liquid intraday data and more common on daily bars.