util: add iterfile to workaround a fileobj.__iter__ issue with EINTR The fileobj.__iter__ implementation in Python 2.7.12 (hg changeset 45d4cea97b04) is buggy: it cannot handle EINTR correctly. In Objects/fileobject.c: size_t Py_UniversalNewlineFread(....) { .... if (!f->f_univ_newline) return fread(buf, 1, n, stream); .... } According to the "fread" man page: If an error occurs, or the end of the file is reached, the return value is a short item count (or zero). Therefore it's possible for "fread" (and "Py_UniversalNewlineFread") to return a positive value while errno is set to EINTR and ferror(stream) changes from zero to non-zero. There are multiple "Py_UniversalNewlineFread": "file_read", "file_readinto", "file_readlines", "readahead". While the first 3 have code to handle the EINTR case, the last one "readahead" doesn't: static int readahead(PyFileObject *f, Py_ssize_t bufsize) { .... chunksize = Py_UniversalNewlineFread( f->f_buf, bufsize, f->f_fp, (PyObject *)f); .... if (chunksize == 0) { if (ferror(f->f_fp)) { PyErr_SetFromErrno(PyExc_IOError); .... } } .... } It means "readahead" could ignore EINTR, if "Py_UniversalNewlineFread" returns a non-zero value. And at the next time "readahead" got executed, if "Py_UniversalNewlineFread" returns 0, "readahead" would raise a Python error without a incorrect errno - could be 0 - thus "IOError: [Errno 0] Error". The only user of "readahead" is "readahead_get_line_skip". The only user of "readahead_get_line_skip" is "file_iternext", aka. "fileobj.__iter__", which should be avoided. There are multiple places where the pattern "for x in fp" is used. This patch adds a "iterfile" method in "util.py" so we can migrate our code from "for x in fp" to "fox x in util.iterfile(fp)".