[Python-Dev] Can I introspect/reflect to get arguments exec()?

[Rocky Bernstein]

[asked on comp.lang.python but no takers. So I'm bumping it up a notch.]

I have ported my Python debugger pydbgr to Python3. See [1] or [2].

Inside the debugger, when there is an exec() somewhere in the call stack,
I'd like to be able to retrieve the string parameter. With this, the
debugger can show part of the string in a call stack. Or it can show the
text when the frame is set to that exec() frame.

Going further, the debugger could write the exec string out to a temporary
file. And when reporting locations, it could report not just something like
"<string> line 4", but also give that temporary file name which a front-end
could use as well.

So consider this code using inspect.getargvalues() and
inspect.currentframe():

    import inspect
    def my_exec(string):
        show_args(inspect.currentframe()) # simulate exec(string)

    def show_args(frame):
        print(inspect.getargvalues(frame))

    my_exec("show_args(inspect.currentframe())")
    exec("show_args(inspect.currentframe())")


When run this is the output:

    python3 exec-args.py
    ArgInfo(args=['string'], varargs=None, keywords=None, locals={'string':
'show_args(inspect.currentframe())'})
    ArgInfo(args=[], varargs=None, keywords=None, locals={'my_exec':
<function my_exec at 0xb6f828ec>,, ...


In a different setting, CPython byte-code assembly that gets generated for
running exec() is:

     25       88 LOAD_GLOBAL            10 (exec)
              91 LOAD_CONST              4
('show_args(inspect.currentframe())')
       -->    94 CALL_FUNCTION           1
              97 POP_TOP

What's going on?

Also, I have the same question for CPython 2.6 or Python 2.7.

Thanks!

[1] http://code.google.com/p/pydbgr/
[2] http://code.google.com/p/python3-trepan/
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