--- a/accessible/xpcom/AccEventGen.py
+++ b/accessible/xpcom/AccEventGen.py
@@ -128,17 +128,17 @@ def print_cpp(idl, fd, conf, eventname):
 
 def print_cpp_file(fd, conf, incdirs):
     idl_paths = set()
     fd.write("/* THIS FILE IS AUTOGENERATED - DO NOT EDIT */\n\n")
     fd.write('#include "xpcAccEvents.h"\n')
 
     includes = []
     for e in conf.simple_events:
-        if not e in includes:
+        if e not in includes:
             includes.append(("nsIAccessible%s" % e))
 
     types = []
     for e in conf.simple_events:
         idl, idl_path = loadEventIDL(p, incdirs, e)
         idl_paths.add(idl_path)
         types.extend(interfaceAttributeTypes(idl))