> The tests for readline() and readlines() expect a TypeError if size is None.
> Calling size.__index__() in this case raises an AttributeError instead. Should I
> change the tests to expect an AttributeError? Alternatively, something like this
> would more closely match the behaviour of the old code:
> 
>     try:
>         size = size.__index__()
>     except AttributeError:
>         raise TypeError("Integer argument expected")

Ah, you're right, TypeError should be raised.