Switch to using black for code formatting (#6361)

* make compatible with pylint and pycodestyle

* black config

* flake8 compatible config

* Missing newline

* Add black check to CI and dev requirements

This commit updates the CI configuration and local tox configuration to
leverage black instead of pycodestyle. It adds a check job to ci and the
tox lint job so we can quickly check if black has been run. A tox job
named 'black' is added to run black on all the code in the repo.

* Run black on everything

This commit reformats all the code in the qiskit-terra repository to use
black. It changes no functionality in the project and just adjusts the
code formatting to be consistent and automated. If you are looking at
this commit in the git log you can likely safely ignore any diff from
this commit as it is just the result of running '`black' on the repo
and instead you should look at any commits before or after this for
functional changes.

Co-authored-by: Lev S. Bishop <18673315+levbishop@users.noreply.github.com>

Author: mtreinish

.pylintrc

@@ -71,7 +71,8 @@ disable=spelling,       # way too noisy
     unnecessary-pass,   # allow for methods with just "pass", for clarity
     no-else-return,     # relax "elif" after a clause with a return
     docstring-first-line-empty, # relax docstring style
-    import-outside-toplevel
+    import-outside-toplevel,
+    bad-continuation, bad-whitespace # differences of opinion with black
 
 
 
@@ -212,7 +213,7 @@ max-nested-blocks=5
 [FORMAT]
 
 # Maximum number of characters on a single line.
-max-line-length=100
+max-line-length=105
 
 # Regexp for a line that is allowed to be longer than the limit.
 ignore-long-lines=^\s*(# )?<?https?://\S+>?$

CONTRIBUTING.md

@@ -18,6 +18,10 @@ please ensure that:
 1. The code follows the code style of the project and successfully
    passes the tests. For convenience, you can execute `tox` locally,
    which will run these checks and report any issues.
+
+   If your code fails the local style checks (specifically the black
+   code formatting check) you can use `tox -eblack` to automatically
+   fix update the code formatting.
 2. The documentation has been updated accordingly. In particular, if a
    function or class has been modified during the PR, please update the
    *docstring* accordingly.
@@ -358,7 +362,24 @@ you just need to update the reference images as follows:
     new tests should now pass.
 
 Note: If you have run `test/ipynb/mpl_tester.ipynb` locally it is possible some file metadata has changed, **please do not commit and push changes to this file unless they were intentional**.
-### Development Cycle
+
+## Style and lint
+
+Qiskit Terra uses 2 tools for verify code formatting and lint checking. The
+first tool is [black](https://github.com/psf/black) which is a code formatting
+tool that will automatically update the code formatting to a consistent style.
+The second tool is [pylint]https://www.pylint.org/) which is a code linter
+which does a deeper analysis of the Python code to find both style issues and
+potential bugs and other common issues in Python.
+
+You can check that your local modifications conform to the style rules
+by running `tox -elint` which will run `black` and `pylint` to check the local
+code formatting and lint. If black returns a code formatting error you can
+run `tox -eblack` to automatically update the code formatting to conform to
+the style. However, if `pylint` returns any error you will have to fix these
+issues by manually updating your code.
+
+## Development Cycle
 
 The development cycle for qiskit-terra is all handled in the open using
 the project boards in Github for project management. We use milestones

Makefile

@@ -51,7 +51,10 @@ lint:
 	python tools/find_optional_imports.py
 
 style:
-	pycodestyle qiskit test
+	black --check qiskit test tools
+
+black:
+	black qiskit test tools
 
 # Use the -s (starting directory) flag for "unittest discover" is necessary,
 # otherwise the QuantumCircuit header will be modified during the discovery.

azure-pipelines.yml

@@ -274,7 +274,7 @@ stages:
         - bash: |
             set -e
             source test-job/bin/activate
-            pycodestyle qiskit test
+            black --check qiskit test tools
             pylint -rn qiskit test
             tools/verify_headers.py qiskit test
             python tools/find_optional_imports.py

pyproject.toml

@@ -1,2 +1,6 @@
 [build-system]
 requires = ["Cython>=0.27.1", "setuptools", "wheel"]
+
+[tool.black]
+line-length = 100
+target-version = ['py36', 'py37', 'py38', 'py39']

qiskit/__init__.py

@@ -64,7 +64,9 @@
     warnings.warn(
         "Using Qiskit with Python 3.6 is deprecated as of the 0.17.0 release. "
         "Support for running Qiskit with Python 3.6 will be removed in a "
-        "future release.", DeprecationWarning)
+        "future release.",
+        DeprecationWarning,
+    )
 
 
 class AerWrapper:
@@ -77,6 +79,7 @@ def __bool__(self):
         if self.aer is None:
             try:
                 from qiskit.providers import aer
+
                 self.aer = aer.Aer
             except ImportError:
                 return False
@@ -86,11 +89,14 @@ def __getattr__(self, attr):
         if not self.aer:
             try:
                 from qiskit.providers import aer
+
                 self.aer = aer.Aer
             except ImportError as exc:
-                raise ImportError('Could not import the Aer provider from the '
-                                  'qiskit-aer package. Install qiskit-aer or '
-                                  'check your installation.') from exc
+                raise ImportError(
+                    "Could not import the Aer provider from the "
+                    "qiskit-aer package. Install qiskit-aer or "
+                    "check your installation."
+                ) from exc
         return getattr(self.aer, attr)
 
 
@@ -104,6 +110,7 @@ def __bool__(self):
         if self.ibmq is None:
             try:
                 from qiskit.providers import ibmq
+
                 self.ibmq = ibmq.IBMQ
             except ImportError:
                 return False
@@ -113,12 +120,15 @@ def __getattr__(self, attr):
         if not self.ibmq:
             try:
                 from qiskit.providers import ibmq
+
                 self.ibmq = ibmq.IBMQ
             except ImportError as exc:
-                raise ImportError('Could not import the IBMQ provider from the '
-                                  'qiskit-ibmq-provider package. Install '
-                                  'qiskit-ibmq-provider or check your  '
-                                  'installation.') from exc
+                raise ImportError(
+                    "Could not import the IBMQ provider from the "
+                    "qiskit-ibmq-provider package. Install "
+                    "qiskit-ibmq-provider or check your  "
+                    "installation."
+                ) from exc
         return getattr(self.ibmq, attr)
 
 

qiskit/algorithms/__init__.py

@@ -165,60 +165,75 @@
 from .variational_algorithm import VariationalAlgorithm, VariationalResult
 from .amplitude_amplifiers import Grover, GroverResult, AmplificationProblem
 from .amplitude_estimators import (
-    AmplitudeEstimator, AmplitudeEstimatorResult,
-    AmplitudeEstimation, AmplitudeEstimationResult,
-    FasterAmplitudeEstimation, FasterAmplitudeEstimationResult,
-    IterativeAmplitudeEstimation, IterativeAmplitudeEstimationResult,
-    MaximumLikelihoodAmplitudeEstimation, MaximumLikelihoodAmplitudeEstimationResult,
-    EstimationProblem
+    AmplitudeEstimator,
+    AmplitudeEstimatorResult,
+    AmplitudeEstimation,
+    AmplitudeEstimationResult,
+    FasterAmplitudeEstimation,
+    FasterAmplitudeEstimationResult,
+    IterativeAmplitudeEstimation,
+    IterativeAmplitudeEstimationResult,
+    MaximumLikelihoodAmplitudeEstimation,
+    MaximumLikelihoodAmplitudeEstimationResult,
+    EstimationProblem,
 )
 from .eigen_solvers import NumPyEigensolver, Eigensolver, EigensolverResult
 from .factorizers import Shor, ShorResult
 from .linear_solvers import HHL, LinearSolver, NumPyLinearSolver, LinearSolverResult
-from .minimum_eigen_solvers import (VQE, VQEResult, QAOA,
-                                    NumPyMinimumEigensolver,
-                                    MinimumEigensolver, MinimumEigensolverResult)
-from .phase_estimators import (HamiltonianPhaseEstimation, HamiltonianPhaseEstimationResult,
-                               PhaseEstimationScale, PhaseEstimation, PhaseEstimationResult)
+from .minimum_eigen_solvers import (
+    VQE,
+    VQEResult,
+    QAOA,
+    NumPyMinimumEigensolver,
+    MinimumEigensolver,
+    MinimumEigensolverResult,
+)
+from .phase_estimators import (
+    HamiltonianPhaseEstimation,
+    HamiltonianPhaseEstimationResult,
+    PhaseEstimationScale,
+    PhaseEstimation,
+    PhaseEstimationResult,
+)
 from .exceptions import AlgorithmError
 
 __all__ = [
-    'AlgorithmResult',
-    'VariationalAlgorithm',
-    'VariationalResult',
-    'AmplificationProblem',
-    'Grover',
-    'GroverResult',
-    'AmplitudeEstimator',
-    'AmplitudeEstimatorResult',
-    'AmplitudeEstimation',
-    'AmplitudeEstimationResult',
-    'FasterAmplitudeEstimation',
-    'FasterAmplitudeEstimationResult',
-    'IterativeAmplitudeEstimation',
-    'IterativeAmplitudeEstimationResult',
-    'MaximumLikelihoodAmplitudeEstimation',
-    'MaximumLikelihoodAmplitudeEstimationResult',
-    'EstimationProblem',
-    'NumPyEigensolver',
-    'LinearSolverResult',
-    'Eigensolver',
-    'EigensolverResult',
-    'Shor',
-    'ShorResult',
-    'VQE',
-    'VQEResult',
-    'QAOA',
-    'LinearSolver',
-    'HHL',
-    'NumPyLinearSolver',
-    'NumPyMinimumEigensolver',
-    'MinimumEigensolver',
-    'MinimumEigensolverResult',
-    'HamiltonianPhaseEstimation',
-    'HamiltonianPhaseEstimationResult',
-    'PhaseEstimationScale',
-    'PhaseEstimation',
-    'PhaseEstimationResult',
-    'AlgorithmError',
+    "AlgorithmResult",
+    "VariationalAlgorithm",
+    "VariationalResult",
+    "AmplificationProblem",
+    "Grover",
+    "GroverResult",
+    "AmplitudeEstimator",
+    "AmplitudeEstimatorResult",
+    "AmplitudeEstimation",
+    "AmplitudeEstimationResult",
+    "FasterAmplitudeEstimation",
+    "FasterAmplitudeEstimationResult",
+    "IterativeAmplitudeEstimation",
+    "IterativeAmplitudeEstimationResult",
+    "MaximumLikelihoodAmplitudeEstimation",
+    "MaximumLikelihoodAmplitudeEstimationResult",
+    "EstimationProblem",
+    "NumPyEigensolver",
+    "LinearSolverResult",
+    "Eigensolver",
+    "EigensolverResult",
+    "Shor",
+    "ShorResult",
+    "VQE",
+    "VQEResult",
+    "QAOA",
+    "LinearSolver",
+    "HHL",
+    "NumPyLinearSolver",
+    "NumPyMinimumEigensolver",
+    "MinimumEigensolver",
+    "MinimumEigensolverResult",
+    "HamiltonianPhaseEstimation",
+    "HamiltonianPhaseEstimationResult",
+    "PhaseEstimationScale",
+    "PhaseEstimation",
+    "PhaseEstimationResult",
+    "AlgorithmError",
 ]

qiskit/algorithms/algorithm_result.py

@@ -20,20 +20,23 @@
 
 
 class AlgorithmResult(ABC):
-    """ Abstract Base Class for algorithm results."""
+    """Abstract Base Class for algorithm results."""
 
     def __str__(self) -> str:
         result = {}
         for name, value in inspect.getmembers(self):
-            if not name.startswith('_') and \
-                    not inspect.ismethod(value) and not inspect.isfunction(value) and \
-                    hasattr(self, name):
+            if (
+                not name.startswith("_")
+                and not inspect.ismethod(value)
+                and not inspect.isfunction(value)
+                and hasattr(self, name)
+            ):
 
                 result[name] = value
 
         return pprint.pformat(result, indent=4)
 
-    def combine(self, result: 'AlgorithmResult') -> None:
+    def combine(self, result: "AlgorithmResult") -> None:
         """
         Any property from the argument that exists in the receiver is
         updated.
@@ -43,15 +46,18 @@ def combine(self, result: 'AlgorithmResult') -> None:
             TypeError: Argument is None
         """
         if result is None:
-            raise TypeError('Argument result expected.')
+            raise TypeError("Argument result expected.")
         if result == self:
             return
 
         # find any result public property that exists in the receiver
         for name, value in inspect.getmembers(result):
-            if not name.startswith('_') and \
-                    not inspect.ismethod(value) and not inspect.isfunction(value) and \
-                    hasattr(self, name):
+            if (
+                not name.startswith("_")
+                and not inspect.ismethod(value)
+                and not inspect.isfunction(value)
+                and hasattr(self, name)
+            ):
                 try:
                     setattr(self, name, value)
                 except AttributeError:

qiskit/algorithms/amplitude_amplifiers/__init__.py

@@ -17,9 +17,9 @@
 from .grover import Grover, GroverResult
 
 __all__ = [
-    'AmplitudeAmplifier',
-    'AmplitudeAmplifierResult',
-    'AmplificationProblem',
-    'Grover',
-    'GroverResult'
+    "AmplitudeAmplifier",
+    "AmplitudeAmplifierResult",
+    "AmplificationProblem",
+    "Grover",
+    "GroverResult",
 ]

qiskit/algorithms/amplitude_amplifiers/amplification_problem.py

@@ -27,15 +27,17 @@ class AmplificationProblem:
     on the optimal bitstring.
     """
 
-    def __init__(self,
-                 oracle: Union[QuantumCircuit, Statevector],
-                 state_preparation: Optional[QuantumCircuit] = None,
-                 grover_operator: Optional[QuantumCircuit] = None,
-                 post_processing: Optional[Callable[[str], Any]] = None,
-                 objective_qubits: Optional[Union[int, List[int]]] = None,
-                 is_good_state: Optional[Union[
-                     Callable[[str], bool], List[int], List[str], Statevector]] = None,
-                 ) -> None:
+    def __init__(
+        self,
+        oracle: Union[QuantumCircuit, Statevector],
+        state_preparation: Optional[QuantumCircuit] = None,
+        grover_operator: Optional[QuantumCircuit] = None,
+        post_processing: Optional[Callable[[str], Any]] = None,
+        objective_qubits: Optional[Union[int, List[int]]] = None,
+        is_good_state: Optional[
+            Union[Callable[[str], bool], List[int], List[str], Statevector]
+        ] = None,
+    ) -> None:
         r"""
         Args:
             oracle: The oracle reflecting about the bad states.
@@ -159,15 +161,17 @@ def is_good_state(self) -> Callable[[str], bool]:
             if all(isinstance(good_bitstr, str) for good_bitstr in self._is_good_state):
                 return lambda bitstr: bitstr in self._is_good_state
             else:
-                return lambda bitstr: all(bitstr[good_index] == '1'  # type:ignore
-                                          for good_index in self._is_good_state)
+                return lambda bitstr: all(
+                    bitstr[good_index] == "1"  # type:ignore
+                    for good_index in self._is_good_state
+                )
 
         return lambda bitstr: bitstr in self._is_good_state.probabilities_dict()
 
     @is_good_state.setter
-    def is_good_state(self,
-                      is_good_state: Union[Callable[[str], bool], List[int], List[str], Statevector]
-                      ) -> None:
+    def is_good_state(
+        self, is_good_state: Union[Callable[[str], bool], List[int], List[str], Statevector]
+    ) -> None:
         """Set the ``is_good_state`` function.
 
         Args:

qiskit/algorithms/amplitude_amplifiers/amplitude_amplifier.py

@@ -25,7 +25,7 @@ class AmplitudeAmplifier(ABC):
     """The interface for amplification algorithms."""
 
     @abstractmethod
-    def amplify(self, amplification_problem: AmplificationProblem) -> 'AmplificationResult':
+    def amplify(self, amplification_problem: AmplificationProblem) -> "AmplificationResult":
         """Run the amplification algorithm.
 
         Args: