Improve readability when printing an ExecutionConfig

[andrijapau]

Feature details

Currently we have,

@qml.qnode(qml.device("default.qubit", wires=1))
def circuit(x):
    qml.RX(x, 0)
    return qml.expval(qml.Z(0))

>>> config = qml.workflow.construct_execution_config(circuit, resolve=False)(1)
>>> print(config)
ExecutionConfig(grad_on_execution=False, use_device_gradient=None, use_device_jacobian_product=False, gradient_method='best', gradient_keyword_arguments={}, device_options={}, interface=<Interface.JAX: 'jax'>, derivative_order=1, mcm_config=MCMConfig(mcm_method=None, postselect_mode=None), convert_to_numpy=True)

This is very hard to read and could lead to debug errors. It would be great to mimic the output we get if we use an external library like pprint. So, something like this,

>>> pprint.pprint(config)
ExecutionConfig(grad_on_execution=None,
                use_device_gradient=None,
                use_device_jacobian_product=False,
                gradient_method='best',
                gradient_keyword_arguments={},
                device_options={},
                interface=<Interface.AUTO: 'auto'>,
                derivative_order=1,
                mcm_config=MCMConfig(mcm_method=None, postselect_mode=None),
                convert_to_numpy=True)

Very easy to read! 🥰

Implementation

A custom __str__ dunder method would need to be added to the ExecutionConfig class (found here). External libraries like pprint can be used to assist in the formatting of the string.

E.g. something like this should work.

class ExecutionConfig(...):
    ...
    def __str__(self):
        return pprint.pformat(self)

How important would you say this feature is?

1: Not important. Would be nice to have.

Additional information

Please note that some of our tests rely on parsing the string representation of the execution configuration to ensure correct behaviour. This feature will most likely involve modifying some tests to account for the new visualization.