def get_call_function_name(frame):
    """If f_back is looking at a call function, return
    the name for it. Otherwise return None"""
    f_back = frame.f_back
    if not f_back: return None
    if 'CALL_FUNCTION' != Mbytecode.op_at_frame(f_back): return None

    co         = f_back.f_code
    code       = co.co_code
    # labels     = dis.findlabels(code)
    linestarts = dict(dis.findlinestarts(co))
    offset     = f_back.f_lasti
    while offset >= 0:
        if offset in linestarts:
            op = code[offset]
            offset += 1
            arg = code[offset]
            # FIXME: put this code in xdis
            extended_arg = 0
            while True:
                if PYTHON_VERSION >= 3.6:
                    if op == opc.EXTENDED_ARG:
                        extended_arg += (arg << 8)
                        continue
                    arg = code[offset] + extended_arg
                    # FIXME: Python 3.6.0a1 is 2, for 3.6.a3 we have 1
                else:
                    if op == opc.EXTENDED_ARG:
                        extended_arg += (arg << 256)
                        continue
                    arg = code[offset] + code[offset+1]*256 + extended_arg
                break

            return co.co_names[arg]
        offset -= 1
        pass
    return None
If f_back is looking at a call function, return
    the name for it. Otherwise return None