Call qc.run_symmetrized_readout in measure_observables

[kylegulshen]

Description

closes #1046. Note that we are still supporting the deprecated readout_symmetrize argument; I'm not sure if this is an appropriate opportunity to drop it?

Checklist

• The above description motivates these changes.
• There is a unit test that covers these changes.
• All new and existing tests pass locally and on Semaphore.
• Parameters have type hints with PEP 484 syntax.
• Functions and classes have useful sphinx-style docstrings.
• The changelog is updated,
  including author and PR number (@username, gh-xxx).

[appleby]

more minor docstring stuff

[karalekas]

Also changelog needs to be updated etc.

[karalekas]

Here's a little snippet that should hopefully explain what I'm thinking!

import warnings
from enum import IntEnum

class SymmetrizationLevel(IntEnum):
    EXHAUSTIVE = -1
    NONE = 0
    ONE = 1
    TWO = 2
    THREE = 3

def fn(level: int = SymmetrizationLevel.EXHAUSTIVE):
    if level is None:
        warnings.warn(f'Providing None to symmetrize_readout is deprecated, setting to {SymmetrizationLevel.NONE}')
        level = SymmetrizationLevel.NONE
    elif isinstance(level, str):
        warnings.warn(f'Providing a string to symmetrize_readout is deprecated, setting to {SymmetrizationLevel.EXHAUSTIVE}')
        level = SymmetrizationLevel.EXHAUSTIVE
    elif level not in list(SymmetrizationLevel):
        raise TypeError(f'The symmetrize_readout argument must be one of the following ints {list(SymmetrizationLevel)}')
    return level

In [2]: fn(4)
---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
<ipython-input-2-90297181a897> in <module>
----> 1 fn(4)

<ipython-input-1-5b7d718a32db> in fn(level)
     17         level = SymmetrizationLevel.EXHAUSTIVE
     18     elif level not in list(SymmetrizationLevel):
---> 19         raise Exception(f'The symmetrize_readout argument must be one of the following ints {list(SymmetrizationLevel)}')
     20     return level
     21

Exception: The symmetrize_readout argument must be one of the following ints [<SymmetrizationLevel.EXHAUSTIVE: -1>, <SymmetrizationLevel.NONE: 0>, <SymmetrizationLevel.ONE: 1>, <SymmetrizationLevel.TWO: 2>, <SymmetrizationLevel.THREE: 3>]

[karalekas]

what happens if someone passes a string that is not "exhaustive"?

[kylegulshen]

I think it matches previous behavior, you just get an error that tells you which values are supported.

[karalekas]

Last batch of nitpicks.