diff --git a/backtester/option.py b/backtester/option.py
index e0c597c..d382aa0 100644
--- a/backtester/option.py
+++ b/backtester/option.py
@@ -1,14 +1,20 @@
 # Option Enum types
 from enum import Enum
 
-Type = Enum("Type", {"CALL": "call", "PUT": "put"})
-Direction = Enum("Direction", {"BUY": "ask", "SELL": "bid"})
+
+class Type(Enum):
+    CALL = 'call'
+    PUT = 'put'
+
+    def __invert__(self):
+        flip = Type.PUT if self == Type.CALL else Type.CALL
+        return flip
 
 
-def flip(enum_type):
-    """Returns the other value of `Type` or `Direction`"""
-    assert isinstance(enum_type, Type) or isinstance(enum_type, Direction)
+class Direction(Enum):
+    BUY = 'ask'
+    SELL = 'bid'
 
-    for e in type(enum_type):
-        if e != enum_type:
-            return e
+    def __invert__(self):
+        flip = Direction.SELL if self == Direction.BUY else Direction.SELL
+        return flip
diff --git a/backtester/strategy/strategy.py b/backtester/strategy/strategy.py
index 34c5d2a..a5c1223 100644
--- a/backtester/strategy/strategy.py
+++ b/backtester/strategy/strategy.py
@@ -3,7 +3,6 @@ from collections import namedtuple
 import pandas as pd
 
 from backtester.datahandler import Schema
-from backtester.option import flip
 from .strategy_leg import StrategyLeg
 from .signal import Signal, get_order
 
@@ -95,7 +94,7 @@ class Strategy:
                 price = leg.direction.value
             else:
                 flt = leg.exit_filter
-                price = flip(leg.direction).value
+                price = (~leg.direction).value
 
             df = flt(data)
             fields = {