Hello, Here's example: Traceback (most recent call last): File "pseudoc_tool.py", line 91, in <module> first_class_function_value(func, **pass_params) TypeError: print() got an unexpected keyword argument 'noann' Ok, which "print" do you mean, dear CPython? I have a dozen of print functions (mostly methods) around. So I now need to reduce to printf debugging to find which one is actually meant. And what if that happens in 3rd-party library installed in /usr/lib? On a production system? The most interesting fact is that despite functions has always been first-class values and 30-years language history, such issues are still there. I'm fixing this right away in my Pycopy dialect, because while it's minimalist and I tremble over each half-byte added, but it's Python first of all, and Python means good error reporting. Well, actually I don't fix it right away, but work around, put putting source loc in TypeError's error message. And here's an idea of what the real fix should be: The fact that CPython (and Pycopy) sets up function's frame "outside" the function execution is an implementation detail. The model of execution should be: there's a CALL_FUNCTION/CALL_FUNCTION_KW opcode, and after it executes, the context switches to the target function, and that's *when* argument checking happens. That would give the desired behavior that the last entry in traceback is the actual function which was called and which failed parameter checks. Again, it's an implementation detail if some project doesn't do it like that, and performs param checking before actually pointing VM at the new bytecode function (from which location traceback will be automatically constructed). If it does that, it just still need to append an additional traceback entry pointing to the beginning of the target function. I now implemented that too, and now everything makes sense: Traceback (most recent call last): File "pseudoc_tool.py", line 91, in <module> File "../xforms.py", line 25, in print TypeError: unexpected keyword argument 'noann' -- Best regards, Paul mailto:pmiscml@gmail.com