Add and change some docstrings for a better quality (#174)

* Small change.

* First check.

* Typo.

* Add link.

* Change.

* Change.

* Update pennylane_qiskit/qiskit_device.py

* Update from review.

* Typo

* Update docstring transpiler.

* Update.

Co-authored-by: antalszava <[email protected]>

pennylane_qiskit/__init__.py

@@ -16,8 +16,8 @@
 from ._version import __version__
 from .aer import AerDevice
 from .basic_aer import BasicAerDevice
-from .converter import load, load_qasm, load_qasm_from_file
 from .ibmq import IBMQDevice
+from .converter import load, load_qasm, load_qasm_from_file
 from .runtime_devices import IBMQCircuitRunnerDevice
 from .runtime_devices import IBMQSamplerDevice
 from .vqe_runtime_runner import vqe_runner, upload_vqe_runner, delete_vqe_runner

pennylane_qiskit/ibmq.py

@@ -53,6 +53,9 @@ class IBMQDevice(QiskitDevice):
             variable ``IBMQX_URL`` is used, followed by the default URL.
         noise_model (NoiseModel): NoiseModel Object from ``qiskit.providers.aer.noise``.
             Only applicable for simulator backends.
+        hub (str): Name of the provider hub.
+        group (str): Name of the provider group.
+        project (str): Name of the provider project.
     """
 
     short_name = "qiskit.ibmq"

pennylane_qiskit/qiskit_device.py

@@ -49,7 +49,6 @@
     "T": ex.TGate,
     "SX": ex.SXGate,
     "Identity": ex.IGate,
-    # Adding the following for conversion compatibility
     "CSWAP": ex.CSwapGate,
     "CRX": ex.CRXGate,
     "CRY": ex.CRYGate,
@@ -64,7 +63,7 @@
 }
 
 # Separate dictionary for the inverses as the operations dictionary needs
-# to be invertable for the conversion functionality to work
+# to be invertible for the conversion functionality to work
 QISKIT_OPERATION_INVERSES_MAP = {k + ".inv": v for k, v in QISKIT_OPERATION_MAP.items()}
 
 
@@ -78,7 +77,7 @@ class QiskitDevice(QubitDevice, abc.ABC):
         provider (Provider): The Qiskit simulation provider
         backend (str): the desired backend
         shots (int or None): number of circuit evaluations/random samples used
-            to estimate expectation values and variances of observables. For statevector backends,
+            to estimate expectation values and variances of observables. For state vector backends,
             setting to ``None`` results in computing statistics like expectation values and variances analytically.
 
     Keyword Args:
@@ -131,14 +130,14 @@ def __init__(self, wires, provider, backend, shots=1024, **kwargs):
         self.backend_name = backend
         self._capabilities["backend"] = [b.name() for b in self.provider.backends()]
 
-        # check that the backend exists
+        # Check that the backend exists
         if backend not in self._capabilities["backend"]:
             raise ValueError(
                 f"Backend '{backend}' does not exist. Available backends "
                 f"are:\n {self._capabilities['backend']}"
             )
 
-        # perform validation against backend
+        # Perform validation against backend
         b = self.backend
         if len(self.wires) > b.configuration().n_qubits:
             raise ValueError(
@@ -151,7 +150,7 @@ def __init__(self, wires, provider, backend, shots=1024, **kwargs):
         self.process_kwargs(kwargs)
 
     def process_kwargs(self, kwargs):
-        """Processing the keyword arguments that were provided upon device creation.
+        """Processing the keyword arguments that were provided upon device initialization.
 
         Args:
             kwargs (dict): keyword arguments to be set for the device
@@ -181,15 +180,24 @@ def process_kwargs(self, kwargs):
         self.run_args.update(kwargs)
 
     def set_transpile_args(self, **kwargs):
-        """The transpile argument setter."""
+        """The transpile argument setter.
+
+        Keyword Args:
+            kwargs (dict): keyword arguments to be set for the Qiskit transpiler. For more details, see the
+                `Qiskit transpiler documentation <https://qiskit.org/documentation/stubs/qiskit.compiler.transpile.html>`_
+        """
         transpile_sig = inspect.signature(transpile).parameters
         self.transpile_args = {arg: kwargs[arg] for arg in transpile_sig if arg in kwargs}
         self.transpile_args.pop("circuits", None)
         self.transpile_args.pop("backend", None)
 
     @property
     def backend(self):
-        """The Qiskit simulation backend object."""
+        """The Qiskit simulation backend object.
+
+        Returns:
+            qiskit.providers.backend: Qiskit backend object.
+        """
         if self._backend is None:
             self._backend = self.provider.get_backend(self.backend_name)
         return self._backend
@@ -290,7 +298,15 @@ def apply_operations(self, operations):
         return circuits
 
     def qubit_state_vector_check(self, operation, par, wires):
-        """Input check for the the QubitStateVector operation."""
+        """Input check for the the QubitStateVector operation.
+
+        Args:
+            operation (pennylane.Operation): operation to be checked
+
+        Raises:
+            DeviceError: If the operation is QubitStateVector
+            ValueError: If the state has not the right length
+        """
         if operation == "QubitStateVector":
             if "unitary" in self.backend_name:
                 raise DeviceError(
@@ -312,7 +328,11 @@ def compile(self):
         return compiled_circuits
 
     def run(self, qcirc):
-        """Run the compiled circuit, and query the result."""
+        """Run the compiled circuit and query the result.
+
+        Args:
+            qcirc (qiskit.QuantumCircuit): the quantum circuit to be run on the backend
+        """
         self._current_job = self.backend.run(qcirc, shots=self.shots, **self.run_args)
         result = self._current_job.result()
 
@@ -324,7 +344,7 @@ def _get_state(self, result, experiment=None):
 
         Args:
             result (qiskit.Result): result object
-            experiment (str): the name of the experiment to get the state for
+            experiment (str or None): the name of the experiment to get the state for.
 
         Returns:
             array[float]: size ``(2**num_wires,)`` statevector
@@ -349,7 +369,7 @@ def generate_samples(self, circuit=None):
         :math:`q_0` is the most significant bit.
 
         Args:
-            circuit (str): the name of the circuit to get the state for
+            circuit (str or None): the name of the circuit to get the state for
 
         Returns:
              array[complex]: array of samples in the shape ``(dev.shots, dev.num_wires)``