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RC2_IND_SERIES_CAPACITY

Series <name> capacity references an unknown Param <capacity>.

What it means

Series(lookback) is well-formed — the capacity is a bare name, which is exactly the shape the language wants. The problem is that no Param called lookback is declared in this class.

The check is separate from RC2_IND_SERIES because the failure is different in kind: the syntax is right, the binding is missing. And the binding is what matters — the capacity is resolved to the Param’s live value, so a name that resolves to nothing would leave the buffer, and the indicator’s warmup, with no size at all.

Why it happens

A rename that only landed on one side, or a buffer copied in from another indicator that had a differently-named Param:

class MySMA(Indicator):
    position = ON_CHART
    period = Param(20, min=2, max=200)
    buffer = Series(lookback)             # ❌ the Param is called 'period'


    def compute(self, close):
        self.buffer.add(close)
        return sum(self.buffer) / len(self.buffer)

Note what it is not: a plain state field is no substitute. lookback = 20 in the class body declares persistent state, not a Param, and a Series sized from it raises this same error.

How to fix it

Use the Param’s name — or declare the Param the buffer was written for.

class MySMA(Indicator):
    position = ON_CHART
    lookback = Param(20, min=2, max=200)
    buffer = Series(lookback)


    def compute(self, close):
        self.buffer.add(close)
        return sum(self.buffer) / len(self.buffer)

Several buffers may share one Param, and each may carry its own offset:

class Spread(Indicator):
    position = OFF_CHART
    period = Param(20, min=2, max=200)
    highs = Series(period)
    lows = Series(period + 1)


    def compute(self, high, low):
        self.highs.add(high)
        self.lows.add(low)
        return sum(self.highs) / len(self.highs) - sum(self.lows) / len(self.lows)