Add string representation for PassManagerConfig

[mtreinish]

Summary

This commit adds a new string representation to the PassManagerConfig
class. When str() is run on a PassManagerConfig object it will return a
string listing the values for all of the attributes in the class.

Details and comments

[coveralls]

Pull Request Test Coverage Report for Build 2391198920

• 8 of 9 (88.89%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 84.389%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/transpiler/passmanager_config.py	8	9	88.89%

Totals
Change from base Build 2387377019:	0.02%
Covered Lines:	54551
Relevant Lines:	64642

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💛 - Coveralls

[jakelishman]

Happy to approve if you're not bothered about the comment.

[jakelishman]

I don't feel very strongly about this at all, but is it worth formatting it as

f"""
PassManagerConfig(
    initial_layout={self.initial_layout},
    basis_gates={self.basis_gates},
...
)
"""

so it can easily be copy-paste evaled back into an interpreter?

[mtreinish]

I'm not sure if it's useful to do that in this case because this is not actually going to be a repr string in this case. You won't be able to eval the output because several of the fields are more complex objects that have human readable outputs (InstructionScheduleMap, InstructionDurations, CouplingMap, Target, etc)

I personally was just looking for something that I could use for quick print debugging in #7789 that gave me output I could read to show what was getting passed to the PassManagerConfig

[jakelishman]

I'm fine with this - what I was suggesting is more like for repr anyway.

[1ucian0]

While trying to test it, I realised that I'm not sure if does what is intended:

from qiskit import QuantumRegister
from qiskit.test.mock import FakeMelbourne
from qiskit.transpiler.passmanager_config import PassManagerConfig

qr = QuantumRegister(4, "qr")
initial_layout = [None, qr[0], qr[1], qr[2], None, qr[3]]

backend = FakeMelbourne()
config = PassManagerConfig.from_backend(
    backend, basis_gates=["user_gate"], initial_layout=initial_layout
)

print(config)

Pass Manager Config:
	initial_layout: [None, Qubit(QuantumRegister(4, 'qr'), 0), Qubit(QuantumRegister(4, 'qr'), 1), Qubit(QuantumRegister(4, 'qr'), 2), None, Qubit(QuantumRegister(4, 'qr'), 3)]
	basis_gates: ['user_gate']
	inst_map: None
	coupling_map: [[1, 0], [1, 2], [2, 3], [4, 3], [4, 10], [5, 4], [5, 6], [5, 9], [6, 8], [7, 8], [9, 8], [9, 10], [11, 3], [11, 10], [11, 12], [12, 2], [13, 1], [13, 12]]
	layout_method: None
	routing_method: None
	translation_method: None
	scheduling_method: None
	instruction_durations: id(0,): 5.333333333333333e-08 s
id(1,): 5.333333333333333e-08 s
id(2,): 5.333333333333333e-08 s
id(3,): 5.333333333333333e-08 s
id(4,): 5.333333333333333e-08 s
[...]
measure(11,): 3.555555555555555e-06 s
measure(12,): 3.555555555555555e-06 s
measure(13,): 3.555555555555555e-06 s
measure(14,): 3.555555555555555e-06 s

	backend_properties: <qiskit.providers.models.backendproperties.BackendProperties object at 0x1187d6820>
	approximation_degree: None
	seed_transpiler: None
	timing_constraints: None
	unitary_synthesis_method: default
	unitary_synthesis_plugin_config: None
	target: None

[1ucian0]

tagging this as on hold to avoid an accidental merge, given #8085 (comment) and the lack of test. I dont feel very strongly about this, so feel free to remove the tag to dismiss my comment.

[mtreinish]

@1ucian0 I'm not sure what your concern is that's the expected output, it's showing the string output for each element in the pass manager config. What are you expecting the output to look like?

I'll add a test, that was an oversight.

[1ucian0]

For example, instruction_durations are out-of-indent. Also, the output is huge, because the constructor “unfolds” all the backend properties.