I have just verified that this issue affects readlines and readinto methods on Mac OS X as well.  This tells me that rather than patching all the individual methods, maybe Py_UniversalNewlineFread should be fixed instead.  I believe that the current situation where a function that looks like Python API reports errors by setting flags on a FILE object instead of settin the an exception is against python's design.  I suggest changing Py_UniversalNewlineFgets so that if fread returns 0, it checks whether that was due to EOF or an error and sets an exception in a case of an error and always calls clearerr.