Python 2 has a -b command-line option which is undocumented.

It is used by the warnings machinery to decide to warn about (-b) or raise an error (-bb) if someone uses str(bytes) or str(buffer) (explanation courtesy of grep and Python/pythonrun.c).

Are you sure?  (see issue 10471).  I don't see how -b could do anything in python2, since bytes and string are the same there (and, indeed, from command line experimentation it doesn't seem to).

The code definitely is in 2.7.

Python/_warnings.c:861:    if (Py_BytesWarningFlag > 1)
Python/_warnings.c:863:    else if (Py_BytesWarningFlag)
Python/_warnings.c:867:    PyList_SET_ITEM(filters, pos++, create_filter(PyExc_BytesWarning,
Python/sysmodule.c:1257:    SetFlag(Py_BytesWarningFlag);
Python/pythonrun.c:81:int Py_BytesWarningFlag; /* Warn on str(bytes) and str(buffer) */
Include/pydebug.h:14:PyAPI_DATA(int) Py_BytesWarningFlag;
Include/pyerrors.h:178:PyAPI_DATA(PyObject *) PyExc_BytesWarning;
Modules/main.c:285:            Py_BytesWarningFlag++;
Objects/bytearrayobject.c:1003:    if (Py_BytesWarningFlag) {
Objects/bytearrayobject.c:1004:        if (PyErr_WarnEx(PyExc_BytesWarning,
Objects/bytearrayobject.c:1028:        if (Py_BytesWarningFlag && op == Py_EQ) {
Objects/bytearrayobject.c:1029:            if (PyErr_WarnEx(PyExc_BytesWarning,
Objects/exceptions.c:2018: *    BytesWarning extends Warning
Objects/exceptions.c:2020:SimpleExtendsException(PyExc_Warning, BytesWarning,
Objects/exceptions.c:2110:    PRE_INIT(BytesWarning)
Objects/exceptions.c:2178:    POST_INIT(BytesWarning)
Lib/warnings.py:399:    simplefilter(bytes_action, category=BytesWarning, append=1)
Lib/test/test_bytes.py:25:            with test.test_support.check_warnings(('', BytesWarning)):
Lib/test/exception_hierarchy.txt:50:	   +-- BytesWarning
Include/pydebug.h:14:PyAPI_DATA(int) Py_BytesWarningFlag;
Include/pyerrors.h:178:PyAPI_DATA(PyObject *) PyExc_BytesWarning;
Doc/library/warnings.rst:164:* :exc:`BytesWarning` is ignored unless the :option:`-b` option is given once or

rdmurray@hey:~/python/p27>cat temp.py
x = bytes('abc')
print x
print str(x)
rdmurray@hey:~/python/p27>./python -bb temp.py
abc
abc

test_bytes has a branch for -b and passes without it, with -b and with -bb.  I really don’t know.

Even "from __future__ import unicode_literals" doesn't make it do anything.

Perhaps Christian merged it by mistake in [5341b30b1812]?

Nick Coghlan wrote:
> 
> Nick Coghlan <ncoghlan@gmail.com> added the comment:
> 
> Even "from __future__ import unicode_literals" doesn't make it do anything.
> 
> Perhaps Christian merged it by mistake in [5341b30b1812]?

It looks more like some parts were left out in the merge
by accident: The 2.7 code only raises the warning for bytearrays,
not for bytes and buffers, whereas 3.2 issues the warning for
all bytes and bytearray (but not buffers; which makes sense,
since Python 3 no longer has a text buffer interface).

Hi Marc

I tried reproducing this for bytearray using Python 2.7.2 but I can't see a warning.

devel@moses:~$ python --version
Python 2.7.2+
devel@moses:~$ cat test_py.py 
k = range(10)
kb = bytearray(k)
print kb
kb = bytearray("hi")
print kb
devel@moses:~$ python -b test_py.py 
 
hi
devel@moses:~$ python -bb test_py.py 
 
hi

Please correct me if I'm wrong anywhere here. I'd like to work on this.