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RC2_PARAM_DEFAULT

Param '<name>' requires a default value.

What it means

Every Param() needs a default as its first positional argument. The default is not a convenience — it is what the strategy runs with when nobody has tuned it, and it is where the Param’s type comes from: 20 makes an int, 2.0 a float, False a bool. Without it there is no value to backtest with and no type to build the optimizer dimension from.

Why it happens

A Param declared as a placeholder, with the intention of filling it in from the UI later:

class Placeholder(Strategy):
    period = Param()
    trade = Symbol()
    sizing = FixedCapital()


    def execute(self):
        sma = SMA(self.period, on=self.trade)
        if sma.value > 0 and self.trade.is_flat:
            self.buy(self.trade)

Or bounds given without a value — min/max are keywords, and none of them is the default:

class BoundsOnly(Strategy):
    period = Param(min=2, max=200)
    trade = Symbol()
    sizing = FixedCapital()


    def execute(self):
        sma = SMA(self.period, on=self.trade)
        if sma.value > 0 and self.trade.is_flat:
            self.buy(self.trade)

How to fix it

Lead with the value you would run today.

class WithDefault(Strategy):
    period = Param(20, min=2, max=200)
    trade = Symbol()
    sizing = FixedCapital()


    def execute(self):
        sma = SMA(self.period, on=self.trade)
        if sma.value > 0 and self.trade.is_flat:
            self.buy(self.trade)

If the value is not meant to be tunable at all, it doesn’t need to be a Param — a plain literal in the class body (threshold = 35) is a constant, and stays out of the optimizer grid.