add listener to get notified about live events

backtrader/__init__.py

@@ -56,6 +56,7 @@
 from .strategy import *
 
 from .writer import *
+from .listener import *
 
 from .signal import *
 

backtrader/cerebro.py

@@ -312,6 +312,7 @@ def __init__(self):
         self.storecbs = list()
         self.datacbs = list()
         self.signals = list()
+        self.listeners = list()
         self._signal_strat = (None, None, None)
         self._signal_concurrent = False
         self._signal_accumulate = False
@@ -623,6 +624,9 @@ def addwriter(self, wrtcls, *args, **kwargs):
         '''
         self.writers.append((wrtcls, args, kwargs))
 
+    def addlistener(self, lstcls, *args, **kwargs):
+        self.listeners.append((lstcls, args, kwargs))
+
     def addsizer(self, sizercls, *args, **kwargs):
         '''Adds a ``Sizer`` class (and args) which is the default sizer for any
         strategy added to cerebro
@@ -1093,6 +1097,7 @@ def run(self, **kwargs):
             self._dopreload = False
 
         self.runwriters = list()
+        self.runlisteners = list()
 
         # Add the system default writer if requested
         if self.p.writer is True:
@@ -1104,6 +1109,10 @@ def run(self, **kwargs):
             wr = wrcls(*wrargs, **wrkwargs)
             self.runwriters.append(wr)
 
+        for lstcls, lstargs, lstkwargs in self.listeners:
+            wr = lstcls(*lstargs, **lstkwargs)
+            self.runlisteners.append(wr)
+
         # Write down if any writer wants the full csv output
         self.writers_csv = any(map(lambda x: x.p.csv, self.runwriters))
 
@@ -1293,6 +1302,9 @@ def runstrategies(self, iterstrat, predata=False):
             for writer in self.runwriters:
                 writer.start()
 
+            for listener in self.runlisteners:
+                listener.start(self)
+
             # Prepare timers
             self._timers = []
             self._timerscheat = []
@@ -1369,6 +1381,9 @@ def stop_writers(self, runstrats):
             writer.writedict(dict(Cerebro=cerebroinfo))
             writer.stop()
 
+        for listener in self.runlisteners:
+            listener.stop()
+
     def _brokernotify(self):
         '''
         Internal method which kicks the broker and delivers any broker
@@ -1503,6 +1518,13 @@ def _next_writers(self, runstrats):
 
                     writer.next()
 
+    def _next_listeners(self):
+        if not self.runlisteners:
+            return
+
+        for listener in self.runlisteners:
+            listener.next()
+
     def _disable_runonce(self):
         '''API for lineiterators to disable runonce (see HeikinAshi)'''
         self._dorunonce = False
@@ -1650,6 +1672,8 @@ def _runnext(self, runstrats):
 
                     self._next_writers(runstrats)
 
+                self._next_listeners()
+
         # Last notification chance before stopping
         self._datanotify()
         if self._event_stop:  # stop if requested

backtrader/listener.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python
+# -*- coding: utf-8; py-indent-offset:4 -*-
+from __future__ import (absolute_import, division, print_function,
+                        unicode_literals)
+
+import backtrader as bt
+from backtrader.utils.py3 import ( with_metaclass)
+
+
+class ListenerBase(with_metaclass(bt.MetaParams, object)):
+    def next():
+        pass
+
+    def start(self, cerebro):
+        pass
+
+    def stop(self):
+        pass