How to plot
cerebro.plot()
Then 3 observers are automatically added by cerebro, and are controlled with the stdstats parameter (default: True). Do the following to disable them if you wish:
cerebro = bt.Cerebro(stdstats=False)
Plotted Elements
Although the Observers have already been mentioned above in the introduction, they are not the only elements to get plotted. These 3 things get plotted:
Data Feeds added to Cerebro with adddata, replaydata and resampledata
Indicators declared at strategy level (or added to cerebro with addindicator which is purely meant for experimentation purposes and has the indicator added to a dummy strategy)
Observers added to cerebro with addobserver
The Observers are lines objects which run in sync with the strategy and have access to the entire ecosystem, to be able to track things like Cash and Value
Plotting Options
Indicators and Observers have several options that control how they have to be plotted on the chart. There are 3 big groups:
Options affecting the plotting behavior of the entire object
Options affecting the plotting behavior of individual lines
Options affecting the SYSTEM wide plotting options
Object-wide plotting options
plotinfo = dict(plot=True,
subplot=True,
plotname='',
plotskip=False,
plotabove=False,
plotlinelabels=False,
plotlinevalues=True,
plotvaluetags=True,
plotymargin=0.0,
plotyhlines=[],
plotyticks=[],
plothlines=[],
plotforce=False,
plotmaster=None,
plotylimited=True,
)
尽管plotinfo在类定义中给定，但是backtader 中元类的机制，可以让它在多层继承中保持。这意味着：
If a subclass changes for example a value like subplot=True to subplot=False, subclasses further down the hierarchy will have the latter as the default value for subplot
两种设定参数值的方式：
sma = bt.indicators.SimpleMovingAverage(self.data, period=15, plotname='mysma')
sma = bt.indicators.SimpleMovingAverage(self.data, period=15)
sma.plotinfo.plotname = 'mysma'
The meaning of the options
plot: whether the object has to be plotted
subplot: whether to plot along the data or in an independent subchart. Moving Averages are an example of plotting over the data. Stochastic and RSI are examples of things plotted in a subchart on a different scale.
plotname: name to use on the chart instead of the class name. As in the example above mysma instead of SimpleMovingAverage
plotabove: whether to plot above the data. Else plot below. This has only effect if subplot=True
plotlinelabels: whether to plot the names of the individudal lines along the data in the legend on the chart when subplot=False
Example: The Bollinger Bands have 3 lines but the indicator is plotted on top of the data. It seems sensible to have the legend only display a single name like BollingerBands rather than having the name of the 3 individual lines displayed (mid, top, bot)
A use case for this is the BuySell observer for which it makes sense to display the name of the 2 lines and its markers: Buy and Sell to make it clear for the end user what is what.
plotlinevalues: controls whether the legend for the lines in indicators and observers has the last plotted value. Can be controlled on a per-line basis with _plotvalue for each line
plotvaluetags: controls whether a value tag with the last value is plotted on the right hand side of the line. Can be controlled on a per-line basis with _plotvaluetag for each line
plotymargin: margin to add to the top and bottom of individual subcharts on the graph
It is a percentage but 1 based. For example: 0.05 -> 5%
- plothlines: an iterable containing values (within the scale) at which horizontal lines have to be plotted.
This for example helps for the classical indicators with overbought, oversold areas like the RSI which usually has lines plotted at 70 and 30
- plotyticks: an iterable containing values (within the scale) at which value ticks have to specifically be placed on the scale
For example to force the scale to have a 50 to identify the mid point of the scale. Although this seems obvious, the indicators use an auto-scaling mechanism and the 50 may not be obviously be in the centre if an indicator with a 0-100 scale moves between 30-95 on a regular basis.
- plotyhlines: an iterable containing values (within the scale) at which horizontal lines have to be plotted.
This can take over both plothlines and plotyticks.
If none of the above are defined, then where to place horizontal lines and ticks will be entirely controlled by this value
If any of the above are defined they have precedence over the values present in this option
- plotforce: sometimes and thus the complex process of matching data feeds to indicators and bla, bla, bla … a custom indicator may fail to plot. This is a last resort mechanism to try to enforce plotting.
Use it if all else fails
- plotmaster: an Indicator/Observer has a master which is the data on which is working. In some cases plotting it with a different master may be wished needed.
A use case is the PivotPoint indicator which is calculated on Monthly data but is meant for Daily data. It only makes sense to plot it on the daily data which is where the indicator makes sense.
- plotylimited: currently only applies to data feeds. If True (default), other lines on the data plot don’t change the scale. Example: Bollinger Bands (top and bottom) may be far away from the actual absolute minimum/maximum of the data feed. With \plotlimited=True, those bands remain out of the chart, because the data controls the scaling. If set toFalse`, the bands affects the y-scale and become visible on the chart
Line specific plotting options
Indicators/Observers have lines and how this lines are plotted can be influenced with the plotlines object. Most of options specified in plotlines are meant to be directly passed over to matplotlib when plotting. The documentation relies therefore on examples of things that have been done.
Some of the options are controlled directly by backtrader. These all start with an underscore (_):
_plotskip (boolean) which indicates that plotting of a specific line has to be skipped if set to True
_plotvalue (boolean) to control if the legend of this line will contain the last plotted value (default is True)
_plotvaluetag (boolean) to control if a righ hand side tag with the last value is plotted (default is True)
_name (string) which changes the plot name of a specific line
_skipnan (bool, default: False): to skip NaN values when plotting and allowing for example to draw a line between 2 distant points generated by an indicator, which has all intermediate values as NaN (default value for new created data points)
_samecolor (boolean) this forces the next line to have the same color as the previous one avoiding the matplotlib default mechanism of cycling trough a color map for each new plotted element
- _method (string) which chooses the plotting method matplotlib will use for the element. If this is not specified, then the most basic plot method will be chosen.
Example from MACDHisto. Here the histo line is plotted as a bar which is the industry de-facto standard. The following definition can be found in the definition of MACDHisto:
lines = ('histo',)
plotlines = dict(histo=dict(_method='bar', alpha=0.50, width=1.0))
alpha and width are options for matplotlib
- _fill_gt / _fill_lt
Allow filling between the given line and:
Another line
A numeric value
The arguments is an iterable of 2 elements in which:
The 1st argument is a string (name of reference line) or a numeric value
The filling will be done in between the own values and the values of the line or the numeric value
The 2nd argument is either:
A string with a colour name (matplotlib compatible) or hex specification (see matloplit examples)
or
An iterable where the 1st element is the string/hex value for the colour and the second element is a numeric value specifying the alpha transparency (default: 0.20 controlled with fillalpha in a plotting scheme)
Passing options to a not yet known line
Ue the name _X where X stands for a digit in a zero-based index. This means that the options are for line X
A use case from OscillatorMixIn:
plotlines = dict(_0=dict(_name='osc'))
As the name implies, this is a mixin class intended to be used in multiple inheritance schemes (specifically on the right hand side). The mixin has no knowledge of the actual name of the 1st line (index is zero-based) from the other indicator that will be part of the multiple inheritance mix.
And that’s why the options are specified to be for: _0. After the subclassing has taken place the 1st line of the resulting class will have the name osc in plot.
Some plotlines examples
plotlines = dict(
buy=dict(marker='^', markersize=8.0, color='lime', fillstyle='full'),
sell=dict(marker='v', markersize=8.0, color='red', fillstyle='full')
)
...
lines = ('pnlplus', 'pnlminus')
...
plotlines = dict(
pnlplus=dict(_name='Positive',
marker='o', color='blue',
markersize=8.0, fillstyle='full'),
pnlminus=dict(_name='Negative',
marker='o', color='red',
markersize=8.0, fillstyle='full')
)
lines = ('drawdown', 'maxdrawdown',)
...
plotlines = dict(maxdrawdown=dict(_plotskip='True',))
plotlines = dict(
mid=dict(ls='--'),
top=dict(_samecolor=True),
bot=dict(_samecolor=True),
)
lines = ('percK', 'percD',)
...
plotlines = dict(percD=dict(_name='%D', ls='--'),
percK=dict(_name='%K'))
Methods controlling plotting
When dealing with Indicators and Observers the following methods are supported to further control plotting:
_plotlabel(self)
Which should return a list of things to conform the labels which will be placed in between parentheses after the name of the Indicators or Observer （SMA(30)）_plotinit(self)
Which is called at the beginning of plotting to do whatever specific initialization the indicator may need.
System-wide plotting options
First the signature of plot within cerebro:
def plot(self, plotter=None, numfigs=1, iplot=True, **kwargs):
Which means:
- plotter: an object/class containing as attributes the options controlling the system wide plotting
If None is passed a default PlotScheme object (see below) will be instantiated
- numfigs: in how many independent charts a plot has to be broken
Sometimes a chart contains too many bars and will not be easily readable if packed in a single figure. This breaks it down in as many pieces as requested
iplot: automatically plot inline if running inside a Jupyter Notebook
**kwargs: the args will be used to change the values of the attributes of plotter or the default PlotScheme object created if no plotter is passed.
PlotScheme
This object contains all the options that contol system-wide plotting.
