Implement `qml.breakpoint()` and initial integration with `Pdb` #5600

Jaybsoni · 2024-04-30T14:57:24Z

Context:
Part of the effort to add more tools for algorithmic debugging of quantum circuits with PennyLane. In this PR we introduce the qml.breakpoint() function which allows users to insert breakpoints into their quantum workflow and enter a debugging context (via Pdb) to step through their quantum functions.

Description of the Change:

Added a PLDB class which inherits most of its functionality from Pdb.
Added functionality to pass active device information into the debugger during qnode execution to validate the compatibility between the device and the debugger.

github-actions · 2024-04-30T15:09:03Z

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

A one-to-two sentence description of the change. You may include a small working example for new features.
A link back to this PR.
Your name (or GitHub username) in the contributors section.

Jaybsoni · 2024-04-30T15:09:39Z

[sc-62243]

Jaybsoni · 2024-04-30T17:45:47Z

Open Questions:

Do we want to take any specialized actions when users call step down or step up? Restrict it? Raise a warning? (Currently it is allowed and leads the user into complex pennylane internals)
How should we test the breakpoint functionality without triggering the interactive debugger in the test suite? Are there any industry standards here?
I have currently added validation checks for incompatible devices (anything other than lightning.qubit and default.qubit) as well is if the breakpoint is called outside of a qnode execution. Any thoughts on this?

mlxd · 2024-04-30T17:56:12Z

pennylane/debugging.py

+        Args:
+            dev (Union[Device, "qml.devices.Device"]): The active device
+        """
+        cls.__active_dev.append(dev)


So devices are add-only, not not selectively removed --- as in, we expect them to be appended, and reset the entire list to remove?

Yes exactly! In fact, instead of appending, we could probably just override the 1st entry in the list each time, since there shouldn't be more than one "active device" at a time.

mlxd · 2024-04-30T17:58:21Z

pennylane/debugging.py

+    PLDB.valid_context()  # Ensure its being executed in a valid context
+
+    debugger = PLDB()
+    debugger.set_trace(sys._getframe().f_back)  # pylint: disable=protected-access


Is this always guaranteed to work? What happens if I do this from the CLI versus a Jupyter notebook cell --- is the correct frame used in both cases?

I know it works for the CLI and from within a Jupyter-notebook cell. Not sure if it will work with other interactive python sessions.

mlxd · 2024-04-30T18:01:53Z

pennylane/workflow/qnode.py

+        if PLDB.is_active_dev():
+            PLDB.reset_active_dev()
+
+        PLDB.add_device(self.device)


Just a quick check, but this setup shouldn't have any problem with concurrent execution, right? If we in parallel create 2 qnodes with 2 devices, what happens here if they try to modify the class at the same time?

They will most definitely clash! I definitely think this feature should not be used with concurrent execution, I don't know if a user would ever want to actually debug the circuit for 2 qnodes concurrently?

I based this implementation on how the Queuing manger is structured, how does that correspond with concurrent execution

codecov · 2024-04-30T18:14:09Z

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.68%. Comparing base (9c9b6ba) to head (f82ea4d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5600      +/-   ##
==========================================
- Coverage   99.68%   99.68%   -0.01%     
==========================================
  Files         412      412              
  Lines       38666    38447     -219     
==========================================
- Hits        38545    38325     -220     
- Misses        121      122       +1

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trbromley

Thanks @Jaybsoni!

trbromley · 2024-05-01T15:26:04Z

pennylane/debugging.py

+class PLDB(pdb.Pdb):
+    """Custom debugging class integrated with Pdb."""


To confirm, this isn't something users would typically interact with?

Yes exactly! We don't want the user calling the PLDB class at all. In the same way we wouldn't want them to interact with the QueuingManager class for example.

trbromley · 2024-05-01T15:28:31Z

pennylane/debugging.py

+
+
+def breakpoint():
+    """Launch the custom PennyLane debugger."""


What is the plan with docs here - normally PRs should have detailed docs, especially for major user-facing functions like this. Though if we have a story to track a subsequent docs revisit and polish, I'm fine with that too.

There is a story to revisit the docs and polish. I will add a little more detail to the breakpoint docs in this PR, but once all of the functionality (measuring states, queuing gates in debug mode, etc.) are added in the subsequent PRs, then we can finalize its docstring.

Minor point that we can discuss in a docs PR:

We don't have a quickstart (.rst) for debugging yet. And it doesn't seem like we make quickstarts for any of the high level files in the pennylane folder. Maybe there's a question here about whether debugging functionality should go in pennylane/debugging.py or in pennylane/debugging/debugging.py

implement breakpoint()

20eef13

Jaybsoni added the WIP 🚧 Work-in-progress label Apr 30, 2024

Jaybsoni added 2 commits April 30, 2024 13:38

added docstring and tests

c814e7e

Merge branch 'master' into algo_debug_breakpoint

f120900

format

508bb8b

Jaybsoni requested review from soranjh, trbromley and DSGuala April 30, 2024 17:49

Jaybsoni changed the title ~~[WIP] Implement qml.breakpoint() and initial integration with Pdb~~ Implement qml.breakpoint() and initial integration with Pdb Apr 30, 2024

Jaybsoni added review-ready 👌 PRs which are ready for review by someone from the core team. and removed WIP 🚧 Work-in-progress labels Apr 30, 2024

mlxd reviewed Apr 30, 2024

View reviewed changes

trbromley reviewed May 1, 2024

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Jaybsoni added 3 commits May 7, 2024 12:42

Merge branch 'master' into algo_debug_breakpoint

3d7de97

Add missing test coverage

18bffe2

Merge branch 'master' into algo_debug_breakpoint

f82ea4d

Jaybsoni requested review from mlxd and trbromley May 10, 2024 21:02

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Implement `qml.breakpoint()` and initial integration with `Pdb` #5600

Implement `qml.breakpoint()` and initial integration with `Pdb` #5600

Jaybsoni commented Apr 30, 2024 •

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Jaybsoni commented Apr 30, 2024

Jaybsoni commented Apr 30, 2024

mlxd Apr 30, 2024

Jaybsoni May 2, 2024

mlxd Apr 30, 2024

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Jaybsoni May 2, 2024

trbromley May 1, 2024

Jaybsoni May 2, 2024

DSGuala May 2, 2024

		class PLDB(pdb.Pdb):
		"""Custom debugging class integrated with Pdb."""



		def breakpoint():
		"""Launch the custom PennyLane debugger."""

Implement qml.breakpoint() and initial integration with Pdb #5600

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Implement qml.breakpoint() and initial integration with Pdb #5600

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Implement `qml.breakpoint()` and initial integration with `Pdb` #5600

Implement `qml.breakpoint()` and initial integration with `Pdb` #5600

Jaybsoni commented Apr 30, 2024 •

edited

codecov bot commented Apr 30, 2024 •

edited