Allow setting legend names when multiple series values are used in an…

… Indicator kernc#382

backtesting/_plotting.py

@@ -522,10 +522,14 @@ def __eq__(self, other):
             colors = value._opts['color']
             colors = colors and cycle(_as_list(colors)) or (
                 cycle([next(ohlc_colors)]) if is_overlay else colorgen())
-            legend_label = LegendStr(value.name)
+            legends = value._opts['legends']
+            legends = legends and cycle(_as_list(legends))
+            indicator_name = value.name
+            legend_label = LegendStr(indicator_name)
             for j, arr in enumerate(value, 1):
                 color = next(colors)
-                source_name = f'{legend_label}_{i}_{j}'
+                legend_label = next(legends) if legends is not None else legend_label
+                source_name = f'{indicator_name}_{i}_{j}'
                 if arr.dtype == bool:
                     arr = arr.astype(int)
                 source.add(arr, source_name)
@@ -563,9 +567,10 @@ def __eq__(self, other):
                                             line_color='#666666', line_dash='dashed',
                                             line_width=.5))
             if is_overlay:
-                ohlc_tooltips.append((legend_label, NBSP.join(tooltips)))
+                ohlc_tooltips.append((indicator_name, NBSP.join(tooltips)))
             else:
-                set_tooltips(fig, [(legend_label, NBSP.join(tooltips))], vline=True, renderers=[r])
+                set_tooltips(fig, [(indicator_name, NBSP.join(tooltips))],
+                             vline=True, renderers=[r])
                 # If the sole indicator line on this figure,
                 # have the legend only contain text without the glyph
                 if len(value) == 1:

backtesting/backtesting.py

@@ -76,7 +76,7 @@ def _check_params(self, params):
     def I(self,  # noqa: E741, E743
           func: Callable, *args,
           name=None, plot=True, overlay=None, color=None, scatter=False,
-          **kwargs) -> np.ndarray:
+          legends=None, **kwargs) -> np.ndarray:
         """
         Declare indicator. An indicator is just an array of values,
         but one that is revealed gradually in
@@ -105,6 +105,10 @@ def I(self,  # noqa: E741, E743
         If `scatter` is `True`, the plotted indicator marker will be a
         circle instead of a connected line segment (default).
 
+        `legends` can be list or array of string values to represent
+        legends on your indicator chart. By default it's set to None,
+        and `name` is used as legends.
+
         Additional `*args` and `**kwargs` are passed to `func` and can
         be used for parameters.
 
@@ -151,7 +155,7 @@ def init():
                 overlay = ((x < 1.4) & (x > .6)).mean() > .6
 
         value = _Indicator(value, name=name, plot=plot, overlay=overlay,
-                           color=color, scatter=scatter,
+                           color=color, scatter=scatter, legends=legends,
                            # _Indicator.s Series accessor uses this:
                            index=self.data.index)
         self._indicators.append(value)

backtesting/test/_test.py

@@ -771,6 +771,24 @@ def next(self):
                     plot_drawdown=False, plot_equity=False, plot_pl=False, plot_volume=False,
                     open_browser=False)
 
+    def test_indicator_legends(self):
+        class S(Strategy):
+            def init(self):
+                self.I(lambda: (SMA(self.data.Close, 5), SMA(self.data.Close, 10)), overlay=False,
+                       name='Simple Moving Averages', scatter=False, legends=['SMA 5', 'SMA 10'])
+
+            def next(self):
+                pass
+
+        bt = Backtest(GOOG, S)
+        bt.run()
+        with _tempfile() as f:
+            bt.plot(filename=f,
+                    plot_drawdown=False, plot_equity=False, plot_pl=False, plot_volume=False,
+                    open_browser=True)
+            # Give browser time to open before tempfile is removed
+            time.sleep(1)
+
 
 class TestLib(TestCase):
     def test_barssince(self):