Add exporter implementation

Author: thierry-martinez

graphix/qasm3_exporter.py

@@ -0,0 +1,95 @@
+"""Exporter to OpenQASM3."""
+
+from __future__ import annotations
+
+from fractions import Fraction
+from math import pi
+from typing import TYPE_CHECKING
+
+# assert_never added in Python 3.11
+from typing_extensions import assert_never
+
+from graphix.instruction import Instruction, InstructionKind
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
+
+    from graphix import Circuit
+
+
+def circuit_to_qasm3(circuit: Circuit) -> str:
+    """Export circuit instructions to OpenQASM 3.0 representation.
+
+    Returns
+    -------
+    str
+        The OpenQASM 3.0 string representation of the circuit.
+    """
+    return "\n".join(circuit_to_qasm3_lines(circuit))
+
+
+def circuit_to_qasm3_lines(circuit: Circuit) -> Iterator[str]:
+    """Export circuit instructions to line-by-line OpenQASM 3.0 representation.
+
+    Returns
+    -------
+    Iterator[str]
+        The OpenQASM 3.0 lines that represent the circuit.
+    """
+    yield "OPENQASM 3;"
+    yield 'include "stdgates.inc";'
+    yield f"qubit[{circuit.width}] q;"
+    if any(instr.kind == InstructionKind.M for instr in circuit.instruction):
+        yield f"bit[{circuit.width}] b;"
+    for instr in circuit.instruction:
+        yield f"{instruction_to_qasm3(instr)};"
+
+
+def instruction_to_qasm3(instruction: Instruction) -> str:
+    """Get the qasm3 representation of a single circuit instruction."""
+    if instruction.kind == InstructionKind.M:
+        return f"b[{instruction.target}] = measure q[{instruction.target}]"
+    # Use of `==` here for mypy
+    if (
+        instruction.kind == InstructionKind.RX  # noqa: PLR1714
+        or instruction.kind == InstructionKind.RY
+        or instruction.kind == InstructionKind.RZ
+    ):
+        if not isinstance(instruction.angle, float):
+            raise ValueError("QASM export of symbolic pattern is not supported")
+        rad_over_pi = instruction.angle / pi
+        tol = 1e-9
+        frac = Fraction(rad_over_pi).limit_denominator(1000)
+        if abs(rad_over_pi - float(frac)) > tol:
+            angle = f"{rad_over_pi}*pi"
+        num, den = frac.numerator, frac.denominator
+        sign = "-" if num < 0 else ""
+        num = abs(num)
+        if den == 1:
+            angle = f"{sign}pi" if num == 1 else f"{sign}{num}*pi"
+        else:
+            angle = f"{sign}pi/{den}" if num == 1 else f"{sign}{num}*pi/{den}"
+        return f"{instruction.kind.name.lower()}({angle}) q[{instruction.target}]"
+
+    # Use of `==` here for mypy
+    if (
+        instruction.kind == InstructionKind.H  # noqa: PLR1714
+        or instruction.kind == InstructionKind.I
+        or instruction.kind == InstructionKind.S
+        or instruction.kind == InstructionKind.X
+        or instruction.kind == InstructionKind.Y
+        or instruction.kind == InstructionKind.Z
+    ):
+        return f"{instruction.kind.name.lower()} q[{instruction.target}]"
+    if instruction.kind == InstructionKind.CNOT:
+        return f"cx q[{instruction.control}], q[{instruction.target}]"
+    if instruction.kind == InstructionKind.SWAP:
+        return f"swap q[{instruction.targets[0]}], q[{instruction.targets[1]}]"
+    if instruction.kind == InstructionKind.RZZ:
+        return f"rzz q[{instruction.control}], q[{instruction.target}]"
+    if instruction.kind == InstructionKind.CCX:
+        return f"ccx q[{instruction.controls[0]}], q[{instruction.controls[1]}], q[{instruction.target}]"
+    # Use of `==` here for mypy
+    if instruction.kind == InstructionKind._XC or instruction.kind == InstructionKind._ZC:  # noqa: PLR1714
+        raise ValueError("Internal instruction should not appear")
+    assert_never(instruction.kind)

tests/test_qasm3_exporter.py

@@ -0,0 +1,36 @@
+"""Test exporter to OpenQASM3."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+import pytest
+from numpy.random import PCG64, Generator
+
+from graphix.qasm3_exporter import circuit_to_qasm3
+from graphix.random_objects import rand_circuit
+
+try:
+    from graphix_qasm_parser import OpenQASMParser
+except ImportError:
+    pytestmark = pytest.mark.skip(reason="graphix-qasm-parser not installed")
+
+    if TYPE_CHECKING:
+        import sys
+
+        # We skip type-checking the case where there is no
+        # graphix-qasm-parser, since pyright cannot figure out that
+        # tests are skipped in this case.
+        sys.exit(1)
+
+
+@pytest.mark.parametrize("jumps", range(1, 11))
+def test_circuit_to_qasm3(fx_bg: PCG64, jumps: int) -> None:
+    rng = Generator(fx_bg.jumped(jumps))
+    nqubits = 5
+    depth = 4
+    circuit = rand_circuit(nqubits, depth, rng)
+    qasm = circuit_to_qasm3(circuit)
+    parser = OpenQASMParser()
+    parsed_circuit = parser.parse_str(qasm)
+    assert parsed_circuit.instruction == circuit.instruction