[IronPython] Debugging hosted python scripts

Jimmy Schementi jimmy at schementi.com
Thu Mar 31 18:40:13 CEST 2011

If you're interested in building your own debugger, take a look at
Microsoft.Scripting.Debugging.dll gives you APIs for non-blocking
debugging by rewriting the expression tree. This doesn't require the


On Mar 31, 2011, at 12:02 PM, Jeff Hardy <jdhardy at gmail.com> wrote:

> On Wed, Mar 30, 2011 at 8:52 PM, Keith Rome <rome at wintellect.com> wrote:
>> We currently have a line of business application, written entirely in C#,
>> that embeds the IronPython runtime. We offer a GUI script editing
>> environment (using the SyntaxEditor control from Actipro Software, which
>> works great for this). This script editor exists as just another dialog
>> window in our application where the user can extend the business objects
>> behind the application in various ways. The scripts are stored in a
>> database, not in files on the local file system. We have great support for
>> syntax highlighting, compiler error “squiggles”, even Intelliprompt
>> functionality. I am now building live debugging support into our script
>> editor GUI, which is where I have run into some difficulty.
>> I have been going down the path of using ScriptEngine.SetTrace() and
>> inspecting frames in the callback. This works fine if I am not doing
>> anything interactive. For example, dumping some information to
>> Debug.WriteLine(). However what I really need (I think?) is to be able to
>> suspend the script execution during a trace callback. I don’t see a clear
>> way to do this though. The script runtime simply continues execution when my
>> callback returns. I have done some work around running the debugged script
>> on a background thread, and then blocking it during “breakpoint” callbacks –
>> but these scripts are normally run within the UI thread because they
>> interact with data structures that are often databound to UI controls, and
>> running them from a background thread is becoming a minefield of
>> cross-thread violations. I cannot simply run the script in the UI thread,
>> because blocking in the trace callback would make the application
>> unresponsive.
> I think this is going to be your biggest issue with debugging - AFAIK
> the Python engine is not designed to be suspendable; it relies on
> .NET's normal thread suspension mechanism to handle that case. If the
> scripts are on the UI thread, and the debugger is on the UI thread,
> that 's going to be an issue.
> Now, if the engine were running in interpreted mode (i.e. it doesn't
> try to convert Python to IL), it would probably be possible to suspend
> it without suspending the thread, but I have no idea how much work
> that would be. (Heck, it might already support it - Dino?) My hunch is
> that it wouldn't be a huge amount of work, but I'm not familiar with
> the interpreter loop at all.
> - Jeff
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