make ffsim dependency optional

.github/workflows/main.yml

@@ -94,3 +94,29 @@ jobs:
         with:
           name: html_docs
           path: docs/_build/html
+  ffsim:
+    name: tests-ffsim-python${{ matrix.python-version }}-${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        python-version: [3.11]
+        os: ["ubuntu-latest", "macOS-latest"]
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Pip cache
+        uses: actions/cache@v2
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-${{ matrix.python-version }}-pip-tests-${{ hashFiles('setup.py','requirements-dev.txt','constraints.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-${{ matrix.python-version }}-pip-tests-
+            ${{ runner.os }}-${{ matrix.python-version }}-pip-
+            ${{ runner.os }}-${{ matrix.python-version }}
+      - name: Install Deps
+        run: python -m pip install -U tox setuptools virtualenv wheel
+      - name: Run ffsim tests
+        run: tox -e ffsim

qiskit_cold_atom/fermions/__init__.py

@@ -89,20 +89,22 @@
 
 """
 
-from qiskit_cold_atom.fermions.fermion_simulator_backend import FermionSimulator
 from qiskit_cold_atom.fermions.base_fermion_backend import BaseFermionBackend
 from qiskit_cold_atom.fermions.fermion_circuit_solver import FermionCircuitSolver
-
 from qiskit_cold_atom.fermions.fermion_gate_library import (
-    FermionicGate,
-    LoadFermions,
-    Phase,
-    Hop,
-    Interaction,
     FermiHubbard,
+    FermionicGate,
     FRXGate,
     FRYGate,
     FRZGate,
+    Hop,
+    Interaction,
+    LoadFermions,
+    Phase,
 )
+from qiskit_cold_atom.fermions.fermion_simulator_backend import FermionSimulator
 
-from qiskit_cold_atom.fermions.ffsim_backend import FfsimBackend
+try:
+    from qiskit_cold_atom.fermions.ffsim_backend import FfsimBackend
+except ImportError:
+    pass

qiskit_cold_atom/fermions/ffsim_backend.py

@@ -19,7 +19,7 @@
 from collections import Counter
 from typing import Any, Dict, List, Optional, Union
 
-import ffsim
+import ffsim  # pylint: disable=import-error
 import numpy as np
 import scipy.linalg
 from qiskit import QuantumCircuit

qiskit_cold_atom/providers/cold_atom_provider.py

@@ -28,7 +28,6 @@
 from qiskit_cold_atom.exceptions import QiskitColdAtomError
 
 from qiskit_cold_atom.fermions import FermionSimulator
-from qiskit_cold_atom.fermions import FfsimBackend
 from qiskit_cold_atom.spins import SpinSimulator
 
 from qiskit_cold_atom.providers.fermionic_tweezer_backend import (
@@ -40,6 +39,13 @@
 )
 from qiskit_cold_atom.providers.collective_spin_backend import CollectiveSpinSimulator
 
+try:
+    from qiskit_cold_atom.fermions import FfsimBackend
+
+    HAVE_FFSIM = True
+except ImportError:
+    HAVE_FFSIM = False
+
 # Default location of the credentials file
 _DEFAULT_COLDATOM_FILE = os.path.join(
     os.path.expanduser("~"), ".qiskit", "cold_atom_credentials.conf"
@@ -86,8 +92,9 @@ def __init__(self, credentials: Optional[Dict[str, Union[str, List[str]]]] = Non
             SpinSimulator(provider=self),
             FermionicTweezerSimulator(provider=self),
             CollectiveSpinSimulator(provider=self),
-            FfsimBackend(provider=self),
         ]
+        if HAVE_FFSIM:
+            backends.append(FfsimBackend(provider=self))
 
         if credentials is not None:
             try:

requirements.txt

@@ -5,4 +5,3 @@ qiskit-terra>= 0.17.1, <=0.25.2.1
 qiskit-nature>=0.4.4,<=0.6.2
 qiskit-aer>=0.8.0, <=0.12.2
 matplotlib>=3.3
-ffsim==0.0.17

setup.py

@@ -52,6 +52,7 @@
     keywords="qiskit sdk quantum cold atoms",
     packages=setuptools.find_packages(include=["qiskit_cold_atom", "qiskit_cold_atom.*"]),
     install_requires=REQUIREMENTS,
+    extras_require={"ffsim": ["ffsim==0.0.17"]},
     include_package_data=True,
     python_requires=">=3.8",
     zip_safe=False,

test/test_ffsim_backend.py

@@ -13,8 +13,10 @@
 """ffsim backend tests."""
 
 import math
+import unittest
 
 import numpy as np
+from qiskit.test import QiskitTestCase
 
 from qiskit_cold_atom.fermions import (
     FermiHubbard,
@@ -23,7 +25,13 @@
     Interaction,
     Phase,
 )
-from qiskit_cold_atom.fermions.ffsim_backend import FfsimBackend
+
+try:
+    from qiskit_cold_atom.fermions.ffsim_backend import FfsimBackend
+
+    HAVE_FFSIM = True
+except ImportError:
+    HAVE_FFSIM = False
 
 
 def _random_occupations(norb: int, nelec: tuple[int, int], seed=None):
@@ -49,7 +57,8 @@ def _fidelity(counts1: dict[str, int], counts2: dict[str, int]) -> float:
     return result**2
 
 
-class TestFfsimBackend:
+@unittest.skipUnless(HAVE_FFSIM, "requires ffsim")
+class TestFfsimBackend(QiskitTestCase):
     """Test FfsimBackend."""
 
     def test_hop_gate(self):

tox.ini

@@ -33,3 +33,7 @@ skip_install = true
 deps =
 allowlist_externals = rm
 commands = rm -rf {toxinidir}/docs/stubs/ {toxinidir}/docs/_build
+
+[testenv:ffsim]
+deps = .[ffsim]
+commands = python -m unittest test/test_ffsim_backend.py