BUG: Fix assumption that all callables have .__name__

Callable class instances might not. The solution is generic.
Fixes #93

Author: kernc

backtesting/_util.py

@@ -22,7 +22,7 @@ def _as_str(value):
     if name in ('Open', 'High', 'Low', 'Close', 'Volume'):
         return name[:1]
     if callable(value):
-        name = value.__name__.replace('<lambda>', 'λ')
+        name = getattr(value, '__name__', value.__class__.__name__).replace('<lambda>', 'λ')
     if len(name) > 10:
         name = name[:9] + '…'
     return name

backtesting/test/_test.py

@@ -699,13 +699,15 @@ def func():
             pass
 
         class Class:
-            pass
+            def __call__(self):
+                pass
 
         self.assertEqual(_as_str('4'), '4')
         self.assertEqual(_as_str(4), '4')
         self.assertEqual(_as_str(_Indicator([1, 2], name='x')), 'x')
         self.assertEqual(_as_str(func), 'func')
         self.assertEqual(_as_str(Class), 'Class')
+        self.assertEqual(_as_str(Class()), 'Class')
         self.assertEqual(_as_str(pd.Series([1, 2], name='x')), 'x')
         self.assertEqual(_as_str(pd.DataFrame()), 'df')
         self.assertEqual(_as_str(lambda x: x), 'λ')