Many functions use char* where const char* should be used. I've changed this in a few function prototypes which I use while embedding python due to numerous warnings about deprecated casting from string constants to char*.

I was about to submit the very same patch :-)
I missed PyErr_NewException, but you missed the PyMapping_* methods ;)

Please look into this matter. GCC 4.2 has arrived and it has a new
warning. The code:

     char* kwlist[] = { "target", "encoding", NULL };

now gives a warning like:

"warning: deprecated conversion from string constant to ‘char*’"

at least when compiling in C++ mode...

This means that people have to declare it as "const char* kwlist", which
will then trigger another warning when calling
PyArg_ParseTupleAndKeywords with such a variable, because the prototype is:

PyAPI_FUNC(int) PyArg_ParseTupleAndKeywords(PyObject *, PyObject *,
                                                  const char *, char **,
...);

The "char **" should be "const char **". ext-, any chance you could fix
that too?

There was once a rather long discussion about "const" in
PyArg_ParseTupleAndKeywords:
http://mail.python.org/pipermail/python-dev/2006-February/060689.html

If you don't read it to the end, here is the conclusion:
"""
It sounds like the right answer for Python is to change the signature
of PyArg_ParseTupleAndKeywords() back. We'll fix it when C fixes its
const rules <wink>.
"""

"const char*" was accepted without opposition, though.

Douglas Greiman submitted many similar changes with his bpo-2135 patch.
His patch also amends documentation, which is missing here.

I am adding dgreiman to the nosy list here to avoid duplication of
effort.

I am -0 on the idea.

For external APIs visible to user code, this can cause some compatibility problems and users may need to at the very least re-compile this code. So -1 here.

For new external APIs, having const wherever appropriate should be considered on a case by case basis.

For internal code this is a good idea, but I wouldn't go mass-slashing all the code base now replacing char* by const char*. Presenting some examples where this makes sense in particular would be interesting though. +0

For external APIs visible to user code, this can cause some
compatibility problems and users may need to at the very least
re-compile this code.

Can you explain exactly which compatibility problems this would cause?

Actually, the point is precisely to make life easier for third-party code, since "const char *" is more accepting than "char *".

Antoine, I was referring to the discussion linked earlier (http://mail.python.org/pipermail/python-dev/2006-February/060689.html). Users of the C API needed to recompile their code and also add preprocessor hacks to make things compatible with C and C++, AFAIU.

Antoine, I was referring to the discussion linked earlier
(http://mail.python.org/pipermail/python-dev/2006-February/060689.html).

Ok, I've read it through. The problem is specifically with
pointers-to-pointers:
http://mail.python.org/pipermail/python-dev/2006-February/060849.html

And indeed, PyArg_ParseTupleAndKeywords() got its "const char **"
argument changed back to "char **". But the other consts have stayed
(such as the "const char *" argument to the same
PyArg_ParseTupleAndKeywords()).

So it looks like the patch, in essence, is legit.
(of course, in practice, it probably won't apply cleanly, since it's
very old; and perhaps it's incomplete too)

In C++ we may overload functions for backward compatibility:

PyAPI_FUNC(int) PyArg_ParseTupleAndKeywords(PyObject *, PyObject *,
                        const char *, const char * const *, ...);
PyAPI_FUNC(int) PyArg_VaParseTupleAndKeywords(PyObject *, PyObject *,
                        const char *, const char * const *, va_list va);
...
#ifdef __cplusplus
inline int
PyArg_ParseTupleAndKeywords(PyObject *args, PyObject *keywords,
                        const char *format, char * const *kwlist, ...)
{
    int retval;
    va_list va;
    va_start(va, kwlist);
    retval = PyArg_ParseTupleAndKeywords(args, keywords, format,
                        (const char * const *)kwlist, va_start);
    va_end(va);
    return retval;
}
#endif

See also bpo-9369.

The patch is outdated. Some function prototypes were changed in bpo-9369, some were changed before.

Here is a new patch. It adds const qualifier to following public functions:
PyObject_DelAttrString, PyObject_HasAttrString, PyObject_GetAttrString, PyObject_SetAttrString, PyObject_DelItemString, PyMapping_DelItemString, PyMapping_HasKeyString, PyMapping_GetItemString, PyMapping_SetItemString, PyFile_FromFd, PyImport_ExecCodeModule, PyImport_ExecCodeModuleEx, PyImport_ExecCodeModuleWithPathnames, PyImport_ImportFrozenModule, PyLong_FromString, PyOS_strtoul, PyOS_strtol, PyOS_Readline, PyMarshal_ReadObjectFromString, PyParser_ParseFile, PyParser_ParseFileFlags, PyParser_ParseFileFlagsEx, PyTokenizer_FromFile. It also changes prototypes of some internal functions and structures and fixes documentation for PyDict_DelItemString. Some of functions already were documented with const qualifier.

The patch synchronized with tip.

New changeset 3055e61f1e66 by Serhiy Storchaka in branch 'default':
Issue bpo-1772673: The type of char* arguments now changed to const char*.
http://hg.python.org/cpython/rev/3055e61f1e66

Compile errors on OS X 10.8 with clang:

cc -Wno-unused-result -Werror=declaration-after-statement -g -O0 -Wall -Wstrict-prototypes     -I. -IInclude -I../../source/Include    -DPy_BUILD_CORE  -c ../../source/Modules/posixmodule.c -o Modules/posixmodule.o
In file included from ../../source/Modules/posixmodule.c:5959:
/usr/include/util.h:94:5: error: conflicting types for 'openpty'
int     openpty(int *, int *, char *, struct termios *,
        ^
../../source/Include/pyport.h:676:12: note: previous declaration is here
extern int openpty(int *, int *, char *,
           ^
In file included from ../../source/Modules/posixmodule.c:5959:
/usr/include/util.h:97:7: error: conflicting types for 'forkpty'
pid_t   forkpty(int *, char *, struct termios *, struct winsize *);
        ^
../../source/Include/pyport.h:678:14: note: previous declaration is here
extern pid_t forkpty(int *, char *,
             ^
2 errors generated.
make: *** [Modules/posixmodule.o] Error 1

New changeset 8bd69bd6e129 by Serhiy Storchaka in branch 'default':
Restore prototypes for the 'openpty' and 'forkpty' on BSDI (broken in issue bpo-1772673).
http://hg.python.org/cpython/rev/8bd69bd6e129

New changeset 599a957038fa by Serhiy Storchaka in branch 'default':
Removed redundant casts to char *.
https://hg.python.org/cpython/rev/599a957038fa