Remove left-over Python 2-isms

dev_tools/conf/.pylintrc

@@ -19,9 +19,7 @@
 
 [MAIN]
 
-# Analyse import fallback blocks. This can be used to support both Python 2 and
-# 3 compatible code, which means that the block might have code that exists
-# only in one or another interpreter, leading to false positives when analysed.
+# Analyse import fallback blocks.
 analyse-fallback-blocks=no
 
 # Clear in-memory caches upon conclusion of linting. Useful if running pylint
@@ -1027,4 +1025,4 @@ init-import=yes
 
 # List of qualified module names which can have objects that can redefine
 # builtins.
-redefining-builtins-modules=six.moves,past.builtins,future.builtins,builtins,io
+redefining-builtins-modules=builtins,io

src/openfermion/chem/molecular_data.py

@@ -396,7 +396,7 @@ def spinorb_from_spatial(one_body_integrals, two_body_integrals):
     return one_body_coefficients, two_body_coefficients
 
 
-class MolecularData(object):
+class MolecularData:
     """Class for storing molecule data from a fixed basis set at a fixed
     geometry that is obtained from classical electronic structure
     packages. Not every field is filled in every calculation. All data
@@ -859,7 +859,7 @@ def load(self):
             # Load charge:
             self.charge = int(f["charge"][...])
             # Load description:
-            self.description = f["description"][...].tobytes().decode('utf-8').rstrip(u'\x00')
+            self.description = f["description"][...].tobytes().decode('utf-8').rstrip('\x00')
             # Load name:
             self.name = f["name"][...].tobytes().decode('utf-8')
             # Load n_atoms:

src/openfermion/contrib/representability/_dualbasis.py

@@ -2,7 +2,7 @@
 import copy
 
 
-class DualBasisElement(object):
+class DualBasisElement:
     """
     This object is named after the algebraic dual space or dual vector space
 
@@ -154,7 +154,7 @@ def __add__(self, other):
             raise TypeError("DualBasisElement can be added to same type or DualBasis")
 
 
-class DualBasis(object):
+class DualBasis:
     def __init__(self, elements: Optional[Union[None, List[DualBasisElement]]] = None):
         """
         A collection of DualBasisElements

src/openfermion/contrib/representability/_multitensor.py

@@ -3,7 +3,7 @@
 from openfermion.contrib.representability._dualbasis import DualBasisElement, DualBasis
 
 
-class TMap(object):
+class TMap:
     def __init__(self, tensors):
         """
         provide a map of tensor name to tensors
@@ -22,7 +22,7 @@ def __iter__(self):
             yield tt
 
 
-class MultiTensor(object):
+class MultiTensor:
     def __init__(self, tensors, dual_basis=DualBasis()):
         """
         A collection of tensor objects with maps from name to tensor

src/openfermion/contrib/representability/_namedtensor.py

@@ -4,7 +4,7 @@
 from openfermion.contrib.representability._bijections import Bijection, index_index_basis
 
 
-class Tensor(object):
+class Tensor:
     """
     Instantiation of named tensor
     """

src/openfermion/hamiltonians/special_operators_test.py

@@ -173,7 +173,7 @@ def test_init(self):
         # Test 'c' operator
         op1 = majorana_operator((2, 0))
         op2 = majorana_operator('c2')
-        op3 = majorana_operator(u'c2')
+        op3 = majorana_operator('c2')
         correct = FermionOperator('2^') + FermionOperator('2')
         self.assertEqual(op1, op2)
         self.assertEqual(op1, op3)

src/openfermion/linalg/davidson.py

@@ -31,7 +31,7 @@ class DavidsonError(Exception):
     pass
 
 
-class DavidsonOptions(object):
+class DavidsonOptions:
     """Davidson algorithm iteration options."""
 
     def __init__(self, max_subspace=100, max_iterations=300, eps=1e-6, real_only=False):
@@ -68,7 +68,7 @@ def set_dimension(self, dimension):
         self.max_subspace = min(self.max_subspace, dimension + 1)
 
 
-class Davidson(object):
+class Davidson:
     """Davidson algorithm to get the n states with smallest eigenvalues."""
 
     def __init__(self, linear_operator, linear_operator_diagonal, options=None):
@@ -350,7 +350,7 @@ def __init__(self, qubit_operator, n_qubits=None, options=None):
             n_qubits(int): Number of qubits.
             options(DavidsonOptions): Iteration options.
         """
-        super(QubitDavidson, self).__init__(
+        super().__init__(
             generate_linear_qubit_operator(qubit_operator, n_qubits, options),
             get_linear_qubit_operator_diagonal(qubit_operator, n_qubits),
             options=options,
@@ -366,9 +366,7 @@ def __init__(self, sparse_matrix, options=None):
             sparse_matrix(scipy.sparse.spmatrix): A sparse matrix in scipy.
             options(DavidsonOptions): Iteration options.
         """
-        super(SparseDavidson, self).__init__(
-            sparse_matrix, sparse_matrix.diagonal(), options=options
-        )
+        super().__init__(sparse_matrix, sparse_matrix.diagonal(), options=options)
 
 
 def generate_random_vectors(row, col, real_only=False):

src/openfermion/linalg/linear_qubit_operator.py

@@ -23,7 +23,7 @@
 from openfermion.utils.operator_utils import count_qubits
 
 
-class LinearQubitOperatorOptions(object):
+class LinearQubitOperatorOptions:
     """Options for LinearQubitOperator."""
 
     def __init__(self, processes=10, pool=None):
@@ -94,7 +94,7 @@ def __init__(self, qubit_operator, n_qubits=None):
             )
 
         n_hilbert = 2**n_qubits
-        super(LinearQubitOperator, self).__init__(shape=(n_hilbert, n_hilbert), dtype=complex)
+        super().__init__(shape=(n_hilbert, n_hilbert), dtype=complex)
         self.qubit_operator = qubit_operator
         self.n_qubits = n_qubits
 
@@ -156,9 +156,7 @@ def __init__(self, qubit_operator, n_qubits=None, options=None):
         """
         n_qubits = n_qubits or count_qubits(qubit_operator)
         n_hilbert = 2**n_qubits
-        super(ParallelLinearQubitOperator, self).__init__(
-            shape=(n_hilbert, n_hilbert), dtype=complex
-        )
+        super().__init__(shape=(n_hilbert, n_hilbert), dtype=complex)
 
         self.qubit_operator = qubit_operator
         self.n_qubits = n_qubits

src/openfermion/ops/operators/binary_code.py

@@ -73,7 +73,7 @@ class BinaryCodeError(Exception):
     pass
 
 
-class BinaryCode(object):
+class BinaryCode:
     r"""The BinaryCode class provides a representation of an encoding-decoding
     pair for binary vectors of different lengths, where the decoding is allowed
     to be non-linear.

src/openfermion/ops/operators/binary_polynomial.py

@@ -23,7 +23,7 @@ class BinaryPolynomialError(Exception):
     pass
 
 
-class BinaryPolynomial(object):
+class BinaryPolynomial:
     r"""The BinaryPolynomial class provides an analytic representation
     of non-linear binary functions. An instance of this class describes
     a term of binary variables (variables of the values {0,1}, indexed

src/openfermion/ops/operators/binary_polynomial_test.py

@@ -36,7 +36,7 @@ def test_init_string(self):
         self.assertEqual(operator1.terms, [(1,)])
         operator1 = BinaryPolynomial('9 w1 w2 + 5')
         self.assertEqual(str(operator1), '[W1 W2] + [1]')
-        operator1 = BinaryPolynomial(u'9 w1 w2 + 5')
+        operator1 = BinaryPolynomial('9 w1 w2 + 5')
         self.assertEqual(str(operator1), '[W1 W2] + [1]')
 
     def test_none_init(self):

src/openfermion/ops/operators/symbolic_operator_test.py

@@ -155,7 +155,7 @@ def test_many_body_order(self):
 
         op1 = DummyOperator1('0^ 3 5^ 6')
         op2 = op1 + DummyOperator1('8^ 3')
-        op3 = op2 + DummyOperator1(u'1^ 2 3^ 4 5 ')
+        op3 = op2 + DummyOperator1('1^ 2 3^ 4 5 ')
 
         op4 = DummyOperator2('X0 X1 Y3')
         op5 = op4 - DummyOperator2('Z0')

src/openfermion/ops/representations/doci_hamiltonian.py

@@ -86,7 +86,7 @@ def __init__(self, constant, hc, hr1, hr2):
             hr2: The coefficients of ($h^{(r2)}_{p, q}$).
                 This is an n_qubits x n_qubits array of floats.
         """
-        super(DOCIHamiltonian, self).__init__(None)
+        super().__init__(None)
 
         self._n_qubits = hc.shape[0]
         self._constant = constant

src/openfermion/ops/representations/interaction_operator.py

@@ -65,9 +65,7 @@ def __init__(self, constant, one_body_tensor, two_body_tensor):
                 n_qubits numpy array of floats.
         """
         # Make sure nonzero elements are only for normal ordered terms.
-        super(InteractionOperator, self).__init__(
-            {(): constant, (1, 0): one_body_tensor, (1, 1, 0, 0): two_body_tensor}
-        )
+        super().__init__({(): constant, (1, 0): one_body_tensor, (1, 1, 0, 0): two_body_tensor})
 
     @property
     def one_body_tensor(self):

src/openfermion/ops/representations/interaction_rdm.py

@@ -39,9 +39,7 @@ def __init__(self, one_body_tensor, two_body_tensor):
             two_body_tensor: Expectation values
                 <a^\dagger_p a^\dagger_q a_r a_s>.
         """
-        super(InteractionRDM, self).__init__(
-            {(1, 0): one_body_tensor, (1, 1, 0, 0): two_body_tensor}
-        )
+        super().__init__({(1, 0): one_body_tensor, (1, 1, 0, 0): two_body_tensor})
 
     @property
     def one_body_tensor(self):

src/openfermion/ops/representations/polynomial_tensor.py

@@ -92,7 +92,7 @@ def general_basis_change(general_tensor, rotation_matrix, key):
     return transformed_general_tensor
 
 
-class PolynomialTensor(object):
+class PolynomialTensor:
     r"""Class for storing tensor representations of operators that correspond
     with multilinear polynomials in the fermionic ladder operators.
     For instance, in a quadratic Hamiltonian (degree 2 polynomial) which

src/openfermion/ops/representations/quadratic_hamiltonian.py

@@ -79,11 +79,9 @@ def __init__(
 
         # Initialize the PolynomialTensor
         if antisymmetric_part is None:
-            super(QuadraticHamiltonian, self).__init__(
-                {(): constant, (1, 0): combined_hermitian_part}
-            )
+            super().__init__({(): constant, (1, 0): combined_hermitian_part})
         else:
-            super(QuadraticHamiltonian, self).__init__(
+            super().__init__(
                 {
                     (): constant,
                     (1, 0): combined_hermitian_part,

src/openfermion/resource_estimates/pbc/thc/factorizations/kmeans.py

@@ -20,7 +20,7 @@
 """
 
 
-class KMeansCVT(object):
+class KMeansCVT:
     def __init__(self, grid: npt.NDArray, max_iteration: int = 100, threshold: float = 1e-6):
         """Initialize k-means solver to find interpolating points for ISDF.
 

src/openfermion/resource_estimates/utils.py

@@ -137,7 +137,7 @@ def power_two(m: int) -> int:
     return 0
 
 
-class RunSilent(object):
+class RunSilent:
     """Context manager to prevent function writing to stdout/stderr
     e.g. for noisy_function(), wrap it like so
 

src/openfermion/testing/testing_utils.py

@@ -219,7 +219,7 @@ def random_quadratic_hamiltonian(
     return QuadraticHamiltonian(hermitian_mat, antisymmetric_mat, constant, chemical_potential)
 
 
-class EqualsTester(object):
+class EqualsTester:
     """Tests equality against user-provided disjoint equivalence groups."""
 
     def __init__(self, test_case):
@@ -315,7 +315,7 @@ def make_equality_pair(self, factory):
         self.add_equality_group(factory(), factory())
 
 
-class _ClassUnknownToSubjects(object):
+class _ClassUnknownToSubjects:
     """Equality methods should be able to deal with the unexpected."""
 
     def __eq__(self, other):

src/openfermion/testing/testing_utils_test.py

@@ -103,7 +103,7 @@ def test_add_equality_group_not_disjoint(self):
             eq.add_equality_group(1)
 
     def test_add_equality_group_bad_hash(self):
-        class KeyHash(object):
+        class KeyHash:
             def __init__(self, k, h):
                 self._k = k
                 self._h = h
@@ -124,7 +124,7 @@ def __hash__(self):
             eq.add_equality_group(KeyHash('c', 2), KeyHash('c', 3))
 
     def test_add_equality_group_exception_hash(self):
-        class FailHash(object):
+        class FailHash:
             def __hash__(self):
                 raise ValueError('injected failure')
 
@@ -135,7 +135,7 @@ def __hash__(self):
     def test_can_fail_when_forgot_type_check(self):
         eq = EqualsTester(self)
 
-        class NoTypeCheckEqualImplementation(object):
+        class NoTypeCheckEqualImplementation:
             def __init__(self):
                 self.x = 1
 
@@ -151,7 +151,7 @@ def __ne__(self, other):
     def test_fails_hash_is_default_and_inconsistent(self):
         eq = EqualsTester(self)
 
-        class DefaultHashImplementation(object):
+        class DefaultHashImplementation:
             __hash__ = object.__hash__
 
             def __init__(self):
@@ -171,7 +171,7 @@ def __ne__(self, other):
     def test_fails_when_ne_is_inconsistent(self):
         eq = EqualsTester(self)
 
-        class InconsistentNeImplementation(object):
+        class InconsistentNeImplementation:
             def __init__(self):
                 self.x = 1
 
@@ -187,7 +187,7 @@ def __ne__(self, other):
     def test_fails_when_not_reflexive(self):
         eq = EqualsTester(self)
 
-        class NotReflexiveImplementation(object):
+        class NotReflexiveImplementation:
             def __init__(self):
                 self.x = 1
 
@@ -200,7 +200,7 @@ def __eq__(self, other):
     def test_fails_when_not_commutative(self):
         eq = EqualsTester(self)
 
-        class NotCommutativeImplementation(object):
+        class NotCommutativeImplementation:
             def __init__(self, x):
                 self.x = x
 

src/openfermion/utils/operator_utils.py

@@ -11,7 +11,6 @@
 #   limitations under the License.
 """This module provides generic tools for classes in ops/"""
 
-from builtins import map, zip
 import marshal
 import os