Brokers and Orders

Backtrader provides a comprehensive broker simulation system that models real trading conditions including commissions, slippage, margin, and various order types.

Broker Basics

The broker manages:

  • Cash: Available trading capital

  • Value: Total portfolio value (cash + positions)

  • Positions: Current holdings

  • Orders: Order management and execution

cerebro = bt.Cerebro()

# Set initial cash
cerebro.broker.setcash(100000)

# Get current values
cash = cerebro.broker.getcash()
value = cerebro.broker.getvalue()

Commission Models

Percentage Commission

# Simple percentage commission (0.1%)
cerebro.broker.setcommission(commission=0.001)

# Per-trade commission with percentage
cerebro.broker.setcommission(
    commission=0.001,     # 0.1% per trade
    margin=None,          # No margin requirement
    mult=1.0              # Contract multiplier
)

Fixed Commission

# Fixed commission per trade
class FixedCommission(bt.CommInfoBase):
    params = (
        ('commission', 5.0),      # $5 per trade
        ('stocklike', True),
        ('commtype', bt.CommInfoBase.COMM_FIXED),
    )

    def _getcommission(self, size, price, pseudoexec):
        return self.p.commission

cerebro.broker.addcommissioninfo(FixedCommission())

Futures Commission

# Futures with margin and multiplier
cerebro.broker.setcommission(
    commission=2.0,       # $2 per contract
    margin=5000,          # Margin per contract
    mult=10,              # Contract multiplier
    commtype=bt.CommInfoBase.COMM_FIXED
)

Slippage

Slippage simulates the difference between expected and actual execution prices.

# Fixed slippage (price points)
cerebro.broker.set_slippage_fixed(fixed=0.01)

# Percentage slippage
cerebro.broker.set_slippage_perc(perc=0.001)  # 0.1%

# Volume-based slippage
cerebro.broker.set_slippage_perc(
    perc=0.001,
    slip_open=True,       # Apply to open orders
    slip_limit=False,     # Don't apply to limit orders
    slip_match=True,      # Apply to matched orders
    slip_out=False        # Don't slip out of high/low range
)

Order Types

Market Orders

Execute immediately at current market price.

# Buy at market
self.buy()

# Sell at market with size
self.sell(size=100)

Limit Orders

Execute at specified price or better.

# Buy limit order
self.buy(exectype=bt.Order.Limit, price=100.0)

# Sell limit order
self.sell(exectype=bt.Order.Limit, price=110.0, size=50)

Stop Orders

Trigger when price reaches stop level.

# Stop buy (for short covering)
self.buy(exectype=bt.Order.Stop, price=105.0)

# Stop sell (stop loss)
self.sell(exectype=bt.Order.Stop, price=95.0)

Stop-Limit Orders

Combination of stop and limit orders.

# Stop-limit order
self.buy(
    exectype=bt.Order.StopLimit,
    price=105.0,      # Stop trigger price
    plimit=106.0      # Limit price after trigger
)

Bracket Orders

Entry with take-profit and stop-loss.

# Bracket order (entry + stop loss + take profit)
orders = self.buy_bracket(
    price=100.0,          # Entry price (limit)
    stopprice=95.0,       # Stop loss price
    limitprice=110.0,     # Take profit price
    size=100
)

# Returns tuple: (main_order, stop_order, limit_order)

Target Orders

Automatically calculate order size to reach target.

# Target percent of portfolio value
self.order_target_percent(target=0.5)  # 50% of portfolio

# Target size
self.order_target_size(target=100)     # Target 100 shares

# Target value
self.order_target_value(target=10000)  # Target $10,000 position

Order Management

Order Status

def notify_order(self, order):
    if order.status in [order.Submitted, order.Accepted]:
        return  # Order pending

    if order.status == order.Completed:
        if order.isbuy():
            print(f'BUY executed at {order.executed.price:.2f}')
        else:
            print(f'SELL executed at {order.executed.price:.2f}')

    elif order.status == order.Canceled:
        print('Order canceled')
    elif order.status == order.Margin:
        print('Insufficient margin')
    elif order.status == order.Rejected:
        print('Order rejected')

Cancel Orders

# Cancel specific order
self.cancel(order)

# Cancel all pending orders
for order in self.broker.get_orders_open():
    self.cancel(order)

Order Validity

from datetime import datetime, timedelta

# Good Till Date
self.buy(
    exectype=bt.Order.Limit,
    price=100.0,
    valid=datetime.now() + timedelta(days=5)
)

# Good Till Canceled (default)
self.buy(exectype=bt.Order.Limit, price=100.0, valid=None)

# Day order
self.buy(exectype=bt.Order.Limit, price=100.0, valid=bt.Order.DAY)

Position Management

def next(self):
    # Check current position
    if self.position:
        print(f'Position size: {self.position.size}')
        print(f'Average price: {self.position.price}')
        print(f'Current P&L: {self.position.size * (self.data.close[0] - self.position.price)}')

    # Get position for specific data
    pos = self.getposition(self.datas[0])

    # Close all positions
    if self.position:
        self.close()

Margin and Leverage

# Set leverage for futures
cerebro.broker.setcommission(
    commission=0.0,
    margin=10000,         # Margin per contract
    mult=50,              # Contract multiplier (e.g., E-mini S&P)
    leverage=10.0         # Maximum leverage
)

# Check available margin
def next(self):
    available_margin = self.broker.getcash()
    required_margin = self.broker.get_margin_info(self.data)

Cheat-On-Open / Cheat-On-Close

Special execution modes for backtesting convenience:

# Cheat-On-Open: Order placed at bar close, executed at next bar's open
cerebro.broker.set_coo(True)

# Cheat-On-Close: Order placed and executed at current bar's close
# WARNING: Not realistic - used only for specific testing scenarios
cerebro.broker.set_coc(True)

警告

Cheat-On-Close is not realistic and should only be used for testing specific scenarios where you need to simulate executing at the closing price.

Broker Methods Reference

Method

Description

set_cash(cash)

Set initial capital

get_cash()

Get available cash

get_value()

Get total portfolio value

getposition(data)

Get position for a data feed

get_orders_open()

Get list of pending orders

set_slippage_perc(perc)

Set percentage slippage

set_slippage_fixed(fixed)

Set fixed slippage (points)

setcommission(...)

Set commission parameters

set_coo(coo)

Enable Cheat-On-Open

set_coc(coc)

Enable Cheat-On-Close

add_cash(cash)

Add or remove cash (negative value)

Best Practices

  1. Realistic Simulation

    # Include all trading costs
cerebro.broker.setcommission(commission=0.001)
cerebro.broker.set_slippage_perc(perc=0.0005)

  2. Order Tracking

    def __init__(self):
    self.order = None

def next(self):
    if self.order:  # Check if order pending
        return
    # Trading logic here

  3. Risk Management

    def next(self):
    # Check if we have enough cash
    if self.broker.getcash() < 1000:
        return

    # Position sizing
    size = int(self.broker.getvalue() * 0.02 / self.data.close[0])
    if size > 0:
        self.buy(size=size)

See Also