Thanks for the report. In my opinion it's difficult to handle this scenario and as far as I know 2to3 can only do syntax level changes with modular fixers for each case. Since Python is dynamic and there is no static type system available it's difficult to differentiate between a socket object and any other object that has the same API with send and recv methods like below : 

if foo():
    s = Socket()
else:
    s = AnotherSocketAPI()

Hence in this case s might be another object that might have the same interface like Socket expecting string for send and recv. Since there is no static typing in Python it depends on runtime introspection to get it right. I will wait for others opinion on this.