stack_data, executing, and pure_eval

Hi! I’ve recently created a few libraries that are helpful for extracting information from frames and tracebacks, and I think they could be very useful to sentry.

• executing can identify the exact AST node being executed by a frame in many cases. It’s always disappointed me that Python only points to a line in each frame in tracebacks, especially when the expression/statement at fault spans many lines. Sometimes it can be really hard to interpret. Currently executing is used in IPython (in master, unreleased) to highlight the node, here’s what it looks like:

• executing can also infer a function __qualname__ from a code object, meaning your traceback can say lorem/ipsum.py in MyClass.__init__ at line 123 instead of just __init__, which is much more informative.
• pure_eval can safely evaluate certain AST nodes without side effects, so that if the source for a frame contains expressions like self.foo and bar[key] their values can often be shown alongside plain variables.
• stack_data collects data from tracebacks for the purpose of formatting and displaying them. It uses executing and pure_eval and also provides a lot of functionality of its own. For example, in this frame:

there are lines from complex_filter which the user doesn’t need to see, and stack_data knows how to filter those out by only collecting lines which belong in the current scope. I integratedstack_data into IPython which allowed removing a lot of flaky custom introspection code, fixing several bugs and making the code more maintainable.

• stack_data identifies the locations of variables and evaluated expressions in the source lines. An intelligent UI could use this, for example, to allow the user to hover over a variable in source code to see its value rather than scroll through a list to find it.

Overall there are lots of possibilities. What would interest you? I’m willing to make a PR and make any necessary changes to the libraries.

[alexmojaki]

Yes.

[github-actions[bot]]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone … forever!

---

“A weed is but an unloved flower.” ― Ella Wheeler Wilcox 🥀