Step-by-step exec

[Aaron Brady]

On Nov 6, 7:11 am, gregory.liel... at gmail.com wrote:
> On Nov 6, 1:02 pm, "saju.pil... at gmail.com" <saju.pil... at gmail.com>
> wrote:
>
> > On Nov 6, 4:27 pm, gregory.liel... at gmail.com wrote:
>
> > > Hi,
>
> > > I am using a small python file as an input file (defining constants,
> > > parameters, input data, ...) for a python application.
> > > The input file is simply read by an exec statement in a specific
> > > dictionary, and then the application retrieve all the data it need
> > > from the dictionary...
> > > Everything is working nicely, but I'd like to have something a little
> > > bit more robust regarding input file errors: now
> > > any error in the python input script raise an exception and stop the
> > > execution.
> > > What I am trying to do is to execute it "step-by-step", so that I can
> > > capture the exception if one line (or multi-line statement) fails,
> > > print a warning about the failure, and continue the execution fo the
> > > following lines/statements. Of course, an error on one line can
> > > trigger errors in the following lines, but it does not matter in the
> > > application I have in mind, the goal is to parse as much of the input
> > > script as possible, warn about the errors, and check what's inside the
> > > dictionary after the exec.
> > > One way to do it is to read the input script line per line, and exec
> > > each line in turn. However, this is not convenient as it does not
> > > allow multi-line statements, or basic control flow like if - else
> > > statements or loops.
>
> > Do you have control over the input file generation ? If the input file
> > can be easily divided into self sufficient blocks of code, you could
> > read each block in one at a time and do a compile() and exec(). Your
> > input file need not be a full python script too, you could just have
> > token delimited blocks of python code which are read in 1 block at a
> > time and then exec().
>
> > -srp
>
> > > Is there a better way for a step-by-step exec? Syntax errors in the
> > > input script are not really a problem (as it is generated elsewhere,
> > > it is not directly edited by users), although it would be nice to
> > > catch. The biggest problem are runtime errors (attribute error, value
> > > error, ...). Maybe compiling the file into a code object, and
> > > executing this code object step-by-step in a way similar to debug? pdb
> > > module should do something similar....
>
> > > Best regards,
>
> > > Greg.
>
> Thanks for your input!
> I had a similar solution in mind (with continuation comments to be
> able to read multi-line statements, instead of statement delimiters,
> but
> I think your delimiter idea would be easier to implement).
> The only problem is that files generated by current and older version
> of the input generator (which do not have any kind of statement
> delimiter)
> will not be readable, or, if we just consider old file as one big
> statement, will not offer the step-by-step execution. It would work
> nice with new files,
> but the best solution would be something that work also with older
> auto-generated files...
>
> In fact, the error in the input script are mainly caused by version
> mismatch, and the step-by-step approach is
> mainly for improving backward compatibility.
> Having better backward compatibility starting from now on would be
> nice, but having backward compatibility with previous versions would
> be even better ;-)
> contains multi-line statements

Check out the InteractiveConsole and InteractiveInterpreter classes.
Derive a subclass and override the 'push' method.  It's not documented
so you'll have to examine the source to find out exactly when and what
to override.