Enable a minimum set of linters

.github/workflows/lint.yml

@@ -0,0 +1,35 @@
+name: Lint check
+
+on:
+  push:
+    branches:
+      - main
+      - 'stable/**'
+  pull_request:
+    branches:
+      - main
+      - 'stable/**'
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          # reno reads the notes from git history, so `reno lint` needs more than a
+          # shallow clone. The submodule the tests need is not checked out: the lint
+          # environment sets `skip_install`, so nothing here compiles the extension.
+          fetch-depth: 0
+      - name: Set up Python 3.11
+        uses: actions/setup-python@v7
+        with:
+          python-version: '3.11'
+      - name: Install tox
+        run: |
+          python -m pip install --upgrade pip
+          pip install tox
+      - name: Run lint check
+        shell: bash
+        run: |
+          tox -elint

examples/tpb/run_sbd_diag.py

@@ -56,7 +56,7 @@ def parse_args():
         description='Quantum chemistry calculation with CPU/GPU support',
         formatter_class=argparse.ArgumentDefaultsHelpFormatter
     )
-    
+
     # Device selection
     parser.add_argument('--device',
                        choices=['auto', 'cpu',
@@ -68,7 +68,7 @@ def parse_args():
                             'gpu-omp (nvc++ OpenMP target offload) | auto. '
                             'gpu-nvhpc-omp / gpu-nvidia-omp are deprecated '
                             'aliases for gpu-omp.')
-    
+
     # Input files
     parser.add_argument('--fcidump', default='../../vendor/sbd-upstream/data/h2o/fcidump.txt',
                        help='Path to FCIDUMP file')
@@ -84,15 +84,15 @@ def parse_args():
                        help='Load initial wavefunction from file')
     parser.add_argument('--savename', default='',
                        help='Save final wavefunction to file')
-    
+
     # MPI communicator sizes
     parser.add_argument('--adet_comm_size', type=int, default=1,
                        help='Alpha determinant communicator size')
     parser.add_argument('--bdet_comm_size', type=int, default=1,
                        help='Beta determinant communicator size')
     parser.add_argument('--task_comm_size', type=int, default=1,
                        help='Helper communicator size')
-    
+
     # Diagonalization method and convergence
     parser.add_argument('--method', type=int, default=0, choices=[0, 1, 2, 3],
                        help='Diagonalization method: 0=Davidson, 1=Davidson+Ham, 2=Lanczos, 3=Lanczos+Ham')
@@ -104,7 +104,7 @@ def parse_args():
                        help='Convergence tolerance')
     parser.add_argument('--max_time', type=float, default=1e10,
                        help='Maximum time in seconds')
-    
+
     # Initialization and options
     parser.add_argument('--init', type=int, default=0,
                        help='Starting vector. 0 puts unit weight on the FIRST '
@@ -147,11 +147,11 @@ def parse_args():
                        help='Carryover ratio')
     parser.add_argument('--carryover_threshold', '--threshold', type=float, default=0.0, dest='threshold',
                        help='Carryover threshold')
-    
+
     # Determinant representation
     parser.add_argument('--bit_length', type=int, default=20,
                        help='Bit length for determinant representation')
-    
+
     # Output options
     parser.add_argument('--dump_matrix_form_wf', default='',
                        help='Filename to dump wavefunction in matrix form')
@@ -162,13 +162,13 @@ def parse_args():
     parser.add_argument('--max_memory_gb_for_determinants', '--gpu-memory', type=int, default=-1,
                        dest='max_memory_gb_for_determinants',
                        help='Maximum GPU memory in GB for determinants (-1=auto, GPU only)')
-    
+
     return parser.parse_args()
 
 
 def main():
     args = parse_args()
-    
+
     # Import sbd — auto-initializes on first use, but we call init()
     # explicitly here to set the default device from --device flag.
     import sbd
@@ -178,14 +178,14 @@ def main():
 
     rank = sbd.get_rank()
     size = sbd.get_world_size()
-    
+
     if rank == 0:
         print("="*70)
         print("SBD Simplified API - Chemistry Calculation")
         print("="*70)
         sbd.print_info()
         print()
-    
+
     # Configure calculation
     config = sbd.TPB_SBD()
     config.max_it = args.max_it
@@ -211,12 +211,12 @@ def main():
         config.use_precalculated_dets = bool(args.use_precalculated_dets)
     if hasattr(config, 'max_memory_gb_for_determinants'):
         config.max_memory_gb_for_determinants = args.max_memory_gb_for_determinants
-    
+
     if rank == 0:
         print("Configuration:")
         print(f"  Device: {sbd.get_device()}")
         print(f"  Communication: {sbd.get_comm_backend()}")
-        print(f"  Method: Davidson")
+        print("  Method: Davidson")
         print(f"  Max iterations: {config.max_it}")
         print(f"  Tolerance: {config.eps}")
         print(f"  MPI ranks: {size}")
@@ -231,7 +231,7 @@ def main():
                   f"requires task x adet x bdet x helper == ranks exactly, so this "
                   f"will abort in TaskCommunicator with 'MPI Size of twister is not "
                   f"a square of a integer'. Use a multiple of {_grid} ranks.")
-        print(f"\nInput files:")
+        print("\nInput files:")
         print(f"  FCIDUMP: {args.fcidump}")
         print(f"  Alpha dets: {args.adetfile}")
         print()

examples/tpb/run_sqd_sbd.ipynb

@@ -58,7 +58,8 @@
    ],
    "source": [
     "from functools import partial\n",
-    "import json, numpy as np\n",
+    "import json\n",
+    "import numpy as np\n",
     "from pathlib import Path\n",
     "from mpi4py import MPI\n",
     "from pyscf import ao2mo, tools\n",
@@ -517,7 +518,7 @@
     "\n",
     "print()\n",
     "print(f'Final SQD energy:  {result.energy + nuc:.10f} Ha   (electronic {result.energy:.10f} + nuc {nuc:.6f})')\n",
-    "print(f'FCI reference   :  ≈ −76.24 Ha')"
+    "print('FCI reference   :  ≈ −76.24 Ha')"
    ]
   },
   {

pyproject.toml

@@ -63,6 +63,18 @@ notebook-dependencies = [
     "pyscf>=2.9",
 ]
 
+[dependency-groups]
+# The linters live in dependency groups rather than optional-dependencies: they are
+# never installed alongside the package (the lint envs set `skip_install`), so there is
+# no reason to publish them as extras in the wheel metadata.
+style = [
+    "ruff==0.16.9",
+]
+lint = [
+    {include-group = "style"},
+    "reno>=4.1",
+]
+
 [project.urls]
 Homepage = "https://github.com/Qiskit/sbd-eigensolver-python"
 Documentation = "https://github.com/Qiskit/sbd-eigensolver-python"
@@ -76,6 +88,86 @@ packages = ["sbd"]
 package-dir = {sbd = "python"}
 zip-safe = false
 
+[tool.ruff]
+line-length = 100
+src = ["python", "test"]
+target-version = "py311"
+
+[tool.ruff.lint]
+select = [
+    "I",   # isort
+    "E",   # pycodestyle
+    "W",   # pycodestyle
+    "D",   # pydocstyle
+    "F",   # pyflakes
+    "RUF", # ruff
+    "UP",  # pyupgrade
+    "SIM", # flake8-simplify
+    "B",   # flake8-bugbear
+    "A",   # flake8-builtins
+]
+ignore = [
+    "E501", # line too long
+]
+
+[tool.ruff.lint.extend-per-file-ignores]
+"test/**.py" = [
+    "D",  # pydocstyle
+]
+"docs/**/*" = [
+    "E402", # module level import not at top of file
+    "D",    # pydocstyle
+]
+# The examples are written to be read top to bottom, so their helpers carry an
+# explanatory comment rather than a docstring, and the prose uses the same
+# mathematical symbols (alpha, the minus sign, the multiplication sign) as the
+# surrounding discussion.
+"examples/**/*" = [
+    "D",      # pydocstyle
+    "I001",   # unsorted-imports: see the isort note below
+    "RUF001", # ambiguous unicode character in string
+    "RUF003", # ambiguous unicode character in comment
+    "SIM102", # collapsible if: the nesting mirrors the explanation
+]
+# `i, j, k, l` is the FCIDUMP two-electron integral index order, so `l` here is
+# the name the file format uses rather than an ambiguous identifier.
+"python/sbd_solver.py" = [
+    "E741", # ambiguous variable name
+]
+# `__all__` is grouped by topic with comments, which sorting would flatten.
+"python/__init__.py" = [
+    "RUF022", # `__all__` is not sorted
+]
+
+[tool.ruff.lint.isort]
+# The package directory is `python/` but it imports as `sbd` (see
+# `[tool.setuptools] package-dir`), so isort cannot infer that `sbd` is ours and
+# would otherwise group it with the third-party imports.
+#
+# This makes `sbd` its own import group, which isort separates with a blank line.
+# That is what we want in `python/` and `test/`, but in the examples it splits
+# short function-local blocks like `from mpi4py import MPI` next to `import sbd`
+# for no gain, so `I001` is ignored for `examples/` above.
+known-first-party = ["sbd"]
+
+[tool.ruff.lint.pydocstyle]
+convention = "google"
+
+[tool.ruff.lint.flake8-copyright]
+notice-rgx = """
+# This code is a Qiskit project.
+#
+# \\(C\\) Copyright IBM \\d{4}((,\\s)\\d{4})*\\.
+#
+# This code is licensed under the Apache License, Version 2\\.0\\. You may
+# obtain a copy of this license in the LICENSE\\.txt file in the root directory
+# of this source tree or at http\\:\\/\\/www\\.apache\\.org\\/licenses\\/LICENSE\\-2\\.0\\.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals\\.
+"""
+
 [tool.pytest.ini_options]
 testpaths = ["test"]
 # -rs lists the skipped tests and why, which matters here because most of the suite