Add const to several API functions that take char *.

In C++, it's an error to pass a string literal to a char* function
without a const_cast().  Rather than require every C++ extension
module to put a cast around string literals, fix the API to state the
const-ness.

I focused on parts of the API where people usually pass literals:
PyArg_ParseTuple() and friends, Py_BuildValue(), PyMethodDef, the type
slots, etc.  Predictably, there were a large set of functions that
needed to be fixed as a result of these changes.  The most pervasive
change was to make the keyword args list passed to
PyArg_ParseTupleAndKewords() to be a const char *kwlist[].

One cast was required as a result of the changes:  A type object
mallocs the memory for its tp_doc slot and later frees it.
PyTypeObject says that tp_doc is const char *; but if the type was
created by type_new(), we know it is safe to cast to char *.

1 files changed, 3 insertions, 2 deletions

diff --git a/Modules/binascii.c b/Modules/binascii.c
index bfb393f..eab90b3 100644
--- a/Modules/binascii.c
+++ b/Modules/binascii.c
@@ -1032,7 +1032,7 @@ binascii_a2b_qp(PyObject *self, PyObject *args, PyObject *kwargs)
 	unsigned char *data, *odata;
 	unsigned int datalen = 0;
 	PyObject *rv;
-	static char *kwlist[] = {"data", "header", NULL};
+	static const char *kwlist[] = {"data", "header", NULL};
 	int header = 0;
 
 	if (!PyArg_ParseTupleAndKeywords(args, kwargs, "s#|i", kwlist, &data,
@@ -1133,7 +1133,8 @@ binascii_b2a_qp (PyObject *self, PyObject *args, PyObject *kwargs)
 	unsigned int datalen = 0, odatalen = 0;
 	PyObject *rv;
 	unsigned int linelen = 0;
-	static char *kwlist[] = {"data", "quotetabs", "istext", "header", NULL};
+	static const char *kwlist[] = {"data", "quotetabs", "istext",
+                                       "header", NULL};
 	int istext = 1;
 	int quotetabs = 0;
 	int header = 0;