[New-bugs-announce] [issue7545] IO buffering behaviour not properly documented

Pascal Chambon report at bugs.python.org
Sat Dec 19 16:59:11 CET 2009

New submission from Pascal Chambon <chambon.pascal at gmail.com>:

It seems there is an important difference between the doc of the IO
module, and its implementation so far (until todcay trunk revision 76805)

"buffering is an optional integer used to set the buffering policy. By
default full buffering is on. Pass 0 to switch buffering off (only
allowed in binary mode), 1 to set line buffering, and an integer > 1 for
full buffering."
--> actually full buffering only occurs if a negative buffering
parameter is given, else it seems th current value i kept as the buffer
size - eg. if we give "3", buffering will be 3 bytes...
This seems a fine behaviour to me, so this implementation could just be
documented as is.

Only case of full buffering in the C iomodule :
    if (buffering < 0) {
        buffering = DEFAULT_BUFFER_SIZE;
            struct stat st;
            long fileno;
            PyObject *res = PyObject_CallMethod(raw, "fileno", NULL);
            if (res == NULL)
                goto error;

            fileno = PyInt_AsLong(res);
            if (fileno == -1 && PyErr_Occurred())
                goto error;

            if (fstat(fileno, &st) >= 0)
                buffering = st.st_blksize;

assignee: georg.brandl
components: Documentation, IO
messages: 96607
nosy: georg.brandl, pakal
severity: normal
status: open
title: IO buffering behaviour not properly documented
versions: Python 2.6, Python 2.7

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