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:

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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?

pennylane/debugging.py

pennylane/workflow/qnode.py

codecov · 2024-04-30T18:14:09Z

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.67%. Comparing base (fbc2a39) to head (26f28f9).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5600      +/-   ##
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- Coverage   99.68%   99.67%   -0.01%     
==========================================
  Files         416      416              
  Lines       39105    38432     -673     
==========================================
- Hits        38981    38307     -674     
- Misses        124      125       +1

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trbromley

Thanks @Jaybsoni!

pennylane/debugging.py

DSGuala

Looks good to me!

qml.breakpoint() pauses execution ✔️
Tested the commands while debugging (list, next, continue, quit) and they all worked fine. ✔️ One note here: hitting next at the return statement of the circuit puts us into PL internals, but I think that's fine.
Can access internal and external variables from the debugging context ✔️
Can queue additional operations ✔️

Pending for next PRs:

qml.debugging.state()
qml.debugging.expval()
qml.debugging.tape()

I think we can keep this open and merge other PRs into this branch. Having the docs will especially help with PR reviews.

pennylane/debugging.py

pennylane/workflow/qnode.py

Mandrenkov

Neat stuff, @Jaybsoni! I left a few minor comments and suggestions.

pennylane/debugging.py

pennylane/workflow/qnode.py

tests/test_debugging.py

trbromley

No blockers to merging from me! Thanks @Jaybsoni!

pennylane/debugging.py

soranjh

Thanks @Jaybsoni, looks good to me.

Merge branch 'debugging_feature' into algo_debug_breakpoint

pennylane/debugging.py

albi3ro · 2024-06-03T15:16:30Z

pennylane/debugging.py

+ def __init__(self, *args, **kwargs):
+ """Initialize the debugger, and set custom prompt string."""
+ super().__init__(*args, **kwargs)
+ self.prompt = "[pldb]: "


Will this be mutable, or could it be defined via property?

Is there value in making the prompt mutable? I think it's OK for this to be hidden state.

It shouldn't be mutable, I can re-define it as a property. It should be internal anyways

Actually, Pdb complains if we implement it as a property. Leaving it as is.

albi3ro · 2024-06-03T15:21:55Z

pennylane/debugging.py

+class PLDB(pdb.Pdb):
+ """Custom debugging class integrated with Pdb."""
+
+ __active_dev = None


Suggested change

__active_dev = None

__active_dev : Optional[qml.devices.Device] = None

Trying to get better about type-hints throughout pennylane. Helps specify things a little bit more.

Not sure what the PennyLane coding standards say, but in Python 3.9+ you can use:

Suggested change

__active_dev = None

__active_dev: qml.devices.Device | None = None

We'll be supporting 3.9 till after the next release.

Yep. I mean that if we don't support Python 3.8 or lower, we can use the | syntax.

I tried adding the type hint, but its causing circular import issues.

We should be able to get around that issue by using

from typing import TYPE_CHECKING if TYPE_CHECKING: from pennylane.devices import Device

but I'm sure we can leave that as a future enhancement.

albi3ro · 2024-06-03T15:28:45Z

pennylane/workflow/qnode.py

+ # Before constructing the tape, we pass the device to the
+ # debugger to ensure they are compatible if there are any
+ # breakpoints in the circuit


So is this just for checking compatibility? If so, do we need to use a context with an enter-exit just for checking validity?

FWIW I think having a "is this device compatible with breakpoints" function makes sense although I'm not sure it would be too useful here (unless we know ahead of time that the current circuit has a breakpoint).

I think that's the key, we don't need to do validation checks if there are no breakpoints in the circuit. Furthermore, we use the device to execute measurements (see the following PR), so we do need the context.

pennylane/debugging.py

Mandrenkov

Thanks for the updates, @Jaybsoni! 🚀

I especially think the skip change adds good value.

pennylane/debugging.py

Mandrenkov · 2024-06-03T18:52:16Z

pennylane/debugging.py

+ def __init__(self, *args, **kwargs):
+ """Initialize the debugger, and set custom prompt string."""
+ super().__init__(*args, **kwargs)
+ self.prompt = "[pldb]: "


Is there value in making the prompt mutable? I think it's OK for this to be hidden state.

pennylane/debugging.py

tests/test_debugging.py

Co-authored-by: Mikhail Andrenkov <[email protected]>

Merge branch 'debugging_feature' into algo_debug_breakpoint

Mandrenkov

Thanks for addressing the feedback, @Jaybsoni! 🚀

Mandrenkov · 2024-06-05T20:43:48Z

pennylane/debugging.py

+class PLDB(pdb.Pdb):
+ """Custom debugging class integrated with Pdb."""
+
+ __active_dev = None


We should be able to get around that issue by using

from typing import TYPE_CHECKING if TYPE_CHECKING: from pennylane.devices import Device

but I'm sure we can leave that as a future enhancement.

implement breakpoint()

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

Jaybsoni added 2 commits April 30, 2024 13:38

added docstring and tests

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Merge branch 'master' into algo_debug_breakpoint

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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

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

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

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	__active_dev = None
	__active_dev : Optional[qml.devices.Device] = None

	__active_dev = None
	__active_dev: qml.devices.Device \| None = None

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

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 •

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