Add .pylintrc, update dev-requirements.txt, and address some trivial Pylint warnings (#911)

This adds a `.pylintrc` file based on the one from Cirq, with a change
to the line length (80 for this project) and removal of one of the
checks because of a difference in conventions. It also adds `pylint` to
`dev-requirements.txt` (using the same version that Cirq uses). Finally,
it also adjusts a few Python files to address consequent linter
warnings.

Author: mhucka

.pylintrc

@@ -0,0 +1,78 @@
+[MAIN]
+load-plugins=pylint.extensions.docstyle,pylint.extensions.docparams
+max-line-length=88
+ignore-paths=eigen/*,tests/googletest/*
+disable=all
+output-format=colorized
+score=no
+reports=no
+enable=
+    abstract-class-instantiated,
+    anomalous-backslash-in-string,
+    assert-on-tuple,
+    assignment-from-no-return,
+    bad-chained-comparison,
+    bad-indentation,
+    bad-mcs-classmethod-argument,
+    bad-mcs-method-argument,
+    bad-option-value,
+    bad-reversed-sequence,
+    bad-super-call,
+    consider-merging-isinstance,
+    consider-using-f-string,
+    continue-in-finally,
+    dangerous-default-value,
+    deprecated-decorator,
+    docstyle,
+    duplicate-argument-name,
+    expression-not-assigned,
+    f-string-without-interpolation,
+    function-redefined,
+    inconsistent-mro,
+    init-is-generator,
+    line-too-long,
+    lost-exception,
+    method-hidden,
+    missing-kwoa,
+    missing-param-doc,
+    missing-raises-doc,
+    mixed-line-endings,
+    no-value-for-parameter,
+    nonexistent-operator,
+    not-in-loop,
+    pointless-statement,
+    raising-bad-type,
+    raising-format-tuple,
+    redefined-builtin,
+    redefined-slots-in-subclass,
+    return-arg-in-generator,
+    return-in-init,
+    return-outside-function,
+    self-cls-assignment,
+    shadowed-import,
+    simplifiable-condition,
+    simplifiable-if-statement,
+    singleton-comparison,
+    too-many-function-args,
+    trailing-whitespace,
+    undefined-variable,
+    unexpected-keyword-arg,
+    unhashable-dict-key,
+    unnecessary-pass,
+    unnecessary-semicolon,
+    unneeded-not,
+    unreachable,
+    unrecognized-inline-option,
+    unused-import,
+    unused-variable,
+    unused-wildcard-import,
+    use-maxsplit-arg,
+    useless-suppression,
+    using-constant-test,
+    wildcard-import,
+    wrong-import-order,
+    wrong-import-position,
+    yield-outside-function
+
+# Ignore long lines containing urls or pylint directives.
+ignore-long-lines=^(.*#\w*pylint: disable.*|\s*(# )?[<\[\(]?https?://\S+[>\]\)]?)$

dev-requirements.txt

@@ -1,6 +1,7 @@
 cmake~=3.28.1
 black~=25.9.0
 flynt~=1.0
+pylint~=4.0.2
 pytest
 pytest-xdist
 py-cpuinfo

docs/_scripts/build_api_docs.py

@@ -17,7 +17,6 @@
 
 from absl import app
 from absl import flags
-from tensorflow_docs.api_generator import doc_controls
 from tensorflow_docs.api_generator import generate_lib
 from tensorflow_docs.api_generator import public_api
 

qsimcirq/__init__.py

@@ -1,3 +1,4 @@
+# pylint: disable=wrong-import-position
 # Copyright 2019 Google LLC. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,6 +14,7 @@
 # limitations under the License.
 
 import importlib
+
 from qsimcirq import qsim_decide
 
 
@@ -53,10 +55,10 @@ def _load_qsim_custatevec():
 qsim_gpu = _load_qsim_gpu()
 qsim_custatevec = _load_qsim_custatevec()
 
-from .qsim_circuit import add_op_to_opstring, add_op_to_circuit, QSimCircuit
+# Note: the following imports must remain at the bottom of this file.
+
+from qsimcirq._version import __version__
+
+from .qsim_circuit import QSimCircuit, add_op_to_circuit, add_op_to_opstring
 from .qsim_simulator import QSimOptions, QSimSimulator
 from .qsimh_simulator import QSimhSimulator
-
-from qsimcirq._version import (
-    __version__,
-)

qsimcirq/qsim_circuit.py

@@ -12,8 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import warnings
-from typing import Dict, List, Optional, Sequence, Tuple, Union
+from typing import Dict, List, Sequence, Tuple, Union
 
 import cirq
 import numpy as np
@@ -159,7 +158,7 @@ def _translate_MatrixGate(gate: cirq.MatrixGate):
         return qsim.kMatrixGate
     raise NotImplementedError(
         f"Received matrix on {gate.num_qubits()} qubits; "
-        + "only up to 6-qubit gates are supported."
+        "only up to 6-qubit gates are supported."
     )
 
 
@@ -219,17 +218,17 @@ def _control_details(
     assignments = list(gate.control_values.expand())
     if len(qubits) > 1 and len(assignments) > 1:
         raise ValueError(
-            f"Cannot translate controlled gate with multiple assignments for multiple qubits: {gate}"
+            "Cannot translate controlled gate with multiple assignments for "
+            f"multiple qubits: {gate}"
         )
     for q, cvs in zip(qubits, zip(*assignments)):
         if 0 in cvs and 1 in cvs:
             # This qubit does not affect control.
             continue
         elif any(cv not in (0, 1) for cv in cvs):
             raise ValueError(
-                f"Cannot translate control values other than 0 and 1: cvs={cvs}"
-            )
-        # Either 0 or 1 is in cvs, but not both.
+                f"Cannot translate control values other than 0 and 1: {cvs=}"
+            )  # Either 0 or 1 is in cvs, but not both.
         control_qubits.append(q)
         if 0 in cvs:
             control_values.append(0)
@@ -247,7 +246,7 @@ def add_op_to_opstring(
     """Adds an operation to an opstring (observable).
 
     Raises:
-      ValueError if qsim_op is not a single-qubit Pauli (I, X, Y, or Z).
+        ValueError if qsim_op is not a single-qubit Pauli (I, X, Y, or Z).
     """
     qsim_gate = qsim_op.gate
     gate_kind = _cirq_gate_kind(qsim_gate)
@@ -258,7 +257,7 @@ def add_op_to_opstring(
 
     is_controlled = isinstance(qsim_gate, cirq.ControlledGate)
     if is_controlled:
-        raise ValueError(f"OpString ops should not be controlled.")
+        raise ValueError("OpString ops should not be controlled.")
 
     qubits = [qubit_to_index_dict[q] for q in qsim_op.qubits]
     qsim.add_gate_to_opstring(gate_kind, qubits, opstring)
@@ -289,7 +288,7 @@ def add_op_to_circuit(
         if num_targets > 4:
             raise NotImplementedError(
                 f"Received control gate on {num_targets} target qubits; "
-                + "only up to 4-qubit gates are supported."
+                "only up to 4-qubit gates are supported."
             )
 
         qsim_qubits = qubits[qsim_gate.num_controls() :]
@@ -366,8 +365,10 @@ def _resolve_parameters_(
 
     def _check_for_confusion_matrix(self):
         """Checks cirq Circuit for Measurement Gates with confusion matrices.
+
         Returns:
-            Throws a runtime exception if a MeasurementGate with a confusion matrix is included in the circuit
+            Throws a runtime exception if a MeasurementGate with a confusion
+            matrix is included in the circuit.
         """
         confusion_maps_on_measurement_gates = [
             op.gate.confusion_map
@@ -377,14 +378,14 @@ def _check_for_confusion_matrix(self):
         if confusion_maps_on_measurement_gates:
             raise ValueError(
                 "Confusion Matrices are not currently supported in Qsim. "
-                "See https://github.com/quantumlib/Cirq/issues/6305 for latest status"
+                "See https://github.com/quantumlib/Cirq/issues/6305 "
+                "for latest status"
             )
 
     def translate_cirq_to_qsim(
         self, qubit_order: cirq.QubitOrderOrList = cirq.QubitOrder.DEFAULT
     ) -> qsim.Circuit:
-        """
-        Translates this Cirq circuit to the qsim representation.
+        """Translates this Cirq circuit to the qsim representation.
         :qubit_order: Ordering of qubits
         :return: a tuple of (C++ qsim Circuit object, moment boundary
             gate indices)
@@ -436,8 +437,7 @@ def to_matrix(op: cirq.GateOperation):
     def translate_cirq_to_qtrajectory(
         self, qubit_order: cirq.QubitOrderOrList = cirq.QubitOrder.DEFAULT
     ) -> qsim.NoisyCircuit:
-        """
-        Translates this noisy Cirq circuit to the qsim representation.
+        """Translates this noisy Cirq circuit to the qsim representation.
         :qubit_order: Ordering of qubits
         :return: a tuple of (C++ qsim NoisyCircuit object, moment boundary
             gate indices)
@@ -476,15 +476,12 @@ def to_matrix(op: cirq.GateOperation):
                     )
                     ops_by_gate.append(oplist)
                     moment_length = max(moment_length, len(oplist))
-                    pass
                 elif cirq.has_mixture(qsim_op):
                     ops_by_mix.append(qsim_op)
                     moment_length = max(moment_length, 1)
-                    pass
                 elif cirq.has_kraus(qsim_op):
                     ops_by_channel.append(qsim_op)
                     moment_length = max(moment_length, 1)
-                    pass
                 else:
                     raise ValueError(f"Encountered unparseable op: {qsim_op}")