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ExposureRule

ExposureRule caps the total percentage of your portfolio that may be invested at once, across every symbol combined. Where PositionSize sizes one entry and ScalingRule.max_position_percentage caps one symbol's position, ExposureRule is the portfolio-wide backstop — e.g. "never have more than 80% invested, always keep at least 20% as a cash buffer."

from investing_algorithm_framework import ExposureRule

Signature​

ExposureRule(
    max_portfolio_percentage: float,
)
ParameterTypeDescription
max_portfolio_percentagefloatMaximum percentage (0–100] of total portfolio value that may be invested at once, across all positions combined.

Unlike position_sizes/scaling_rules, exposure_rule is portfolio-wide, so a strategy sets a single instance, not a per-symbol list:

class MyStrategy(TradingStrategy):
    symbols = ["BTC", "ETH"]
    exposure_rule = ExposureRule(max_portfolio_percentage=80.0)

How it's enforced​

ExposureRule is enforced by ApplyRiskBudgetPhase, the same phase that already prevents overspending past unallocated cash. Every tick, it computes how much of the portfolio is already invested and tightens the cash available for new OPEN_LONG/SCALE_IN orders to whatever headroom remains under the cap:

already_invested = portfolio_value - unallocated
headroom         = (portfolio_value * max_portfolio_percentage / 100) - already_invested

If the strategy's signals this tick would spend more than headroom, every cash-consuming order is scaled down proportionally (same mechanism used for the plain available-cash check), or dropped entirely if the cap is already reached. Closing orders (CLOSE_LONG, CLOSE_SHORT, SCALE_OUT) are never affected — you can always exit a position regardless of the exposure cap.

Example​

from investing_algorithm_framework import (
    TradingStrategy, PositionSize, ExposureRule, Schedule, TimeUnit,
)


class ConservativeStrategy(TradingStrategy):
    schedule = Schedule.every(2, TimeUnit.HOUR)
    symbols = ["BTC", "ETH"]

    position_sizes = [
        PositionSize(symbol="BTC", percentage_of_portfolio=60.0),
        PositionSize(symbol="ETH", percentage_of_portfolio=60.0),
    ]
    # Even though each position size alone could reach 60%, and both
    # combined would be 120%, the exposure cap keeps total invested
    # value at 80% of the portfolio — orders are scaled down
    # proportionally to fit.
    exposure_rule = ExposureRule(max_portfolio_percentage=80.0)

Interaction With Other Rules​

  • PositionSize — determines how much a single entry wants to spend; ExposureRule is the ceiling across all entries combined, applied after sizing.
  • ScalingRule.max_position_percentage — caps one symbol's total position size; ExposureRule caps the whole portfolio's total invested value across every symbol.
  • Available-cash scaling — ExposureRule tightens the same proportional-scaling mechanism that already prevents spending more than unallocated cash; it never loosens it.

See Also​