PyErr_BadInternalCall() calls _PyErr_BadInternalCall(__FILE__, __LINE__). Since __FILE__ is a string constant, the first argument of _PyErr_BadInternalCall should be a "const char*" instead of a "char*".

This is a follow-up to #4949. Most of the patch from #4949 was applied, but not the change to _PyErr_BadInternalCall on Python 2.

Was already fixed in 84618b2064c1. It is questionable wherever it should be backported to 2.7. Most other "const" additions were applied only to the default branch (see issue25923, issue24436, issue1772673, issue9369, issue16369, issue12173, issue1419652 and many others).

> It is questionable wherever it should be backported to 2.7.

It violates the C++ standard (for extension modules written in C++), so it's clearly a bug.

CPython is written on C and provides C API.

Even if change the signature of one function, this will not help much, because a lot of other functions require "char *" instead of "const char *".

There is small disadvantage of changing the signature in a bugfix release. This will lead to incompatibility of your extension with older bugfix releases.

> CPython is written on C and provides C API.

If you look at the title of https://docs.python.org/2/extending/extending.html clearly C++ extensions are also supported.

> Even if change the signature of one function, this will not help much, because a lot of other functions require "char *" instead of "const char *".

I don't know which functions you mean, I only encountered this problem for PyErr_BadInternalCall().

I should also add that the problem cannot be avoided or worked around for PyErr_BadInternalCall() because it's a CPython header itself which does an illegal conversion of a string constant to char*.

> This will lead to incompatibility of your extension with older bugfix releases.

I don't see why there would be ABI incompatibility. My patch is only adding "const" in the call of a C function.

OK, now I understand. Since _PyErr_BadInternalCall() is private function, we will not break any code. Since it is used only by the PyErr_BadInternalCall() macro and always called with string literal as an argument, C++ user can't use PyErr_BadInternalCall() (without a trick described below). Thus the patch fixes a bug. Thank you Jeroen.

The workaround for unpatched Python 2.7 is to undefine the PyErr_BadInternalCall() macro.

    #undef PyErr_BadInternalCall

There is the PyErr_BadInternalCall() function hidden by the macro. It provides less detailed error message, without file name and line number.

New changeset 0e3526ab6a9b by Serhiy Storchaka in branch '2.7':
Issue #26476: Fixed compilation error when use PyErr_BadInternalCall() in C++.
https://hg.python.org/cpython/rev/0e3526ab6a9b