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

Rocky Bernstein rocky at gnu.org
Wed Mar 27 04:00:55 CET 2013 
On Tue, Mar 26, 2013 at 10:18 PM, Benjamin Peterson <benjamin at python.org>wrote:

> 2013/3/26 Rocky Bernstein <rocky at gnu.org>:
> > [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?
>
> execing something is not the same as calling it, so there are no arguments.
>

Okay. But is the string is still somewhere in the CPython VM stack? (The
result of LOAD_CONST 4 above). Is there a way to pick it up from there? At
the point that we are stopped the exec action hasn't taken place yet.




>
>
> --
> Regards,
> Benjamin
>
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