Don't require Tweedledum for qiskit.circuit.classicalfunction on im…

…port (#9754)

* Don't require Tweedledum for `qiskit.circuit.classicalfunction` on import

* Review feedback

qiskit/circuit/classicalfunction/__init__.py

@@ -91,12 +91,6 @@ def grover_oracle(a: Int1, b: Int1, c: Int1, d: Int1) -> Int1:
 
 """
 
-from qiskit.utils.optionals import HAS_TWEEDLEDUM
-
-HAS_TWEEDLEDUM.require_now("classical function oracles")
-
-# pylint: disable=wrong-import-position
-
 from .classicalfunction import ClassicalFunction
 from .exceptions import (
     ClassicalFunctionParseError,

qiskit/circuit/classicalfunction/boolean_expression.py

@@ -15,13 +15,12 @@
 from os.path import basename, isfile
 from typing import Callable, Optional
 
-from tweedledum import BitVec, BoolFunction  # pylint: disable=import-error
-from tweedledum.synthesis import pkrm_synth  # pylint: disable=import-error
-
 from qiskit.circuit import QuantumCircuit
+from qiskit.utils.optionals import HAS_TWEEDLEDUM
 from .classical_element import ClassicalElement
 
 
+@HAS_TWEEDLEDUM.require_in_instance
 class BooleanExpression(ClassicalElement):
     """The Boolean Expression gate."""
 
@@ -35,6 +34,8 @@ def __init__(self, expression: str, name: str = None, var_order: list = None) ->
                (default: by appearance)
         """
 
+        from tweedledum import BoolFunction  # pylint: disable=import-error
+
         self._tweedledum_bool_expression = BoolFunction.from_expression(
             expression, var_order=var_order
         )
@@ -57,6 +58,8 @@ def simulate(self, bitstring: str) -> bool:
         Returns:
             bool: result of the evaluation.
         """
+        from tweedledum import BitVec  # pylint: disable=import-error
+
         bits = []
         for bit in bitstring:
             bits.append(BitVec(1, bit))
@@ -85,6 +88,7 @@ def synth(
 
         if synthesizer is None:
             from .utils import tweedledum2qiskit  # Avoid an import cycle
+            from tweedledum.synthesis import pkrm_synth  # pylint: disable=import-error
 
             truth_table = self._tweedledum_bool_expression.truth_table(output_bit=0)
             return tweedledum2qiskit(pkrm_synth(truth_table), name=self.name, qregs=qregs)
@@ -107,6 +111,8 @@ def from_dimacs_file(cls, filename: str):
             FileNotFoundError: If filename is not found.
         """
 
+        from tweedledum import BoolFunction  # pylint: disable=import-error
+
         expr_obj = cls.__new__(cls)
         if not isfile(filename):
             raise FileNotFoundError("The file %s does not exists." % filename)

qiskit/circuit/classicalfunction/classical_function_visitor.py

@@ -17,11 +17,11 @@
 import ast
 import _ast
 
-from tweedledum.classical import LogicNetwork  # pylint: disable=import-error
-
+from qiskit.utils.optionals import HAS_TWEEDLEDUM
 from .exceptions import ClassicalFunctionParseError, ClassicalFunctionCompilerTypeError
 
 
+@HAS_TWEEDLEDUM.require_in_instance
 class ClassicalFunctionVisitor(ast.NodeVisitor):
     """Node visitor as defined in https://docs.python.org/3/library/ast.html#ast.NodeVisitor"""
 
@@ -58,6 +58,8 @@ def visit_FunctionDef(self, node):
         # Extend scope with the decorator's names
         scope.update({decorator.id: ("decorator", None) for decorator in node.decorator_list})
 
+        from tweedledum.classical import LogicNetwork  # pylint: disable=import-error
+
         self.scopes.append(scope)
         self._network = LogicNetwork()
         self.extend_scope(node.args)

qiskit/circuit/classicalfunction/classicalfunction.py

@@ -15,18 +15,17 @@
 import ast
 from typing import Callable, Optional
 
-from tweedledum.classical import simulate  # pylint: disable=import-error
-from tweedledum.synthesis import pkrm_synth  # pylint: disable=import-error
-
 from qiskit.circuit import QuantumCircuit, QuantumRegister
 from qiskit.exceptions import QiskitError
+from qiskit.utils.optionals import HAS_TWEEDLEDUM
 from .classical_element import ClassicalElement
 from .classical_function_visitor import ClassicalFunctionVisitor
 from .utils import tweedledum2qiskit
 
 
+@HAS_TWEEDLEDUM.require_in_instance
 class ClassicalFunction(ClassicalElement):
-    """Represent a classical function function and its logic network."""
+    """Represent a classical function and its logic network."""
 
     def __init__(self, source, name=None):
         """Creates a ``ClassicalFunction`` from Python source code in ``source``.
@@ -107,6 +106,8 @@ def simulate(self, bitstring: str) -> bool:
         Returns:
             bool: result of the evaluation.
         """
+        from tweedledum.classical import simulate  # pylint: disable=import-error
+
         return simulate(self._network, bitstring)
 
     def simulate_all(self):
@@ -126,6 +127,8 @@ def simulate_all(self):
     @property
     def truth_table(self):
         """Returns (and computes) the truth table"""
+        from tweedledum.classical import simulate  # pylint: disable=import-error
+
         if self._truth_table is None:
             self._truth_table = simulate(self._network)
         return self._truth_table
@@ -153,6 +156,8 @@ def synth(
         if synthesizer:
             return synthesizer(self)
 
+        from tweedledum.synthesis import pkrm_synth  # pylint: disable=import-error
+
         return tweedledum2qiskit(pkrm_synth(self.truth_table[0]), name=self.name, qregs=qregs)
 
     def _define(self):

qiskit/circuit/classicalfunction/utils.py

@@ -12,9 +12,7 @@
 
 """Internal utils for Classical Function Compiler"""
 
-from tweedledum.ir import Qubit  # pylint: disable=import-error
-from tweedledum.passes import parity_decomp  # pylint: disable=import-error
-
+from qiskit.utils.optionals import HAS_TWEEDLEDUM
 
 from qiskit.circuit import QuantumCircuit
 from qiskit.circuit.library.standard_gates import (
@@ -42,6 +40,7 @@
 }
 
 
+@HAS_TWEEDLEDUM.require_in_call
 def _convert_tweedledum_operator(op):
     base_gate = _QISKIT_OPS.get(op.kind())
     if base_gate is None:
@@ -52,6 +51,8 @@ def _convert_tweedledum_operator(op):
 
     # TODO: need to deal with cbits too!
     if op.num_controls() > 0:
+        from tweedledum.ir import Qubit  # pylint: disable=import-error
+
         qubits = op.qubits()
         ctrl_state = ""
         for qubit in qubits[: op.num_controls()]:
@@ -60,6 +61,7 @@ def _convert_tweedledum_operator(op):
     return base_gate()
 
 
+@HAS_TWEEDLEDUM.require_in_call
 def tweedledum2qiskit(tweedledum_circuit, name=None, qregs=None):
     """Converts a `Tweedledum <https://github.com/boschmitt/tweedledum>`_
     circuit into a Qiskit circuit.
@@ -81,6 +83,8 @@ def tweedledum2qiskit(tweedledum_circuit, name=None, qregs=None):
     else:
         qiskit_qc = QuantumCircuit(tweedledum_circuit.num_qubits(), name=name)
 
+    from tweedledum.passes import parity_decomp  # pylint: disable=import-error
+
     for instruction in parity_decomp(tweedledum_circuit):
         gate = _convert_tweedledum_operator(instruction)
         qubits = [qubit.uid() for qubit in instruction.qubits()]