3.2 Extending a Datafeed

通过一个例子来说明：
读取csv中的pe列并把数据加入到lines中：

from backtrader.feeds import GenericCSVData

class GenericCSV_PE(GenericCSVData):

    # Add a 'pe' line to the inherited ones from the base class
    lines = ('pe',)

    # openinterest in GenericCSVData has index 7 ... add 1
    # add the parameter to the parameters inherited from the base class
    params = (('pe', 8),)

则后续可通过data line的方式调用相关数据：

import backtrader as bt

....

class MyStrategy(bt.Strategy):

    ...

    def next(self):

        if self.data.close > 2000   and self.data.pe < 12:
            # TORA TORA TORA --- Get off this market
            self.sell(stake=1000000, price=0.01, exectype=Order.Limit)
    ...

Backtrader中没有自动打印额外line数据的功能，但是可以通过把line数据放到一个indicator中的方式实现打印，如：

import backtrader as bt
import backtrader.indicators as btind

....

class MyStrategy(bt.Strategy):

    def __init__(self):

        # The indicator autoregisters and will plot even if no obvious
        # reference is kept to it in the class
        btind.SMA(self.data.pe, period=1, subplot=False)

    ...

    def next(self):

        if self.data.close > 2000 and self.data.pe < 12:
            # TORA TORA TORA --- Get off this market
            self.sell(stake=1000000, price=0.01, exectype=Order.Limit)
    ...