QPY load error with backslash in parameter expression #14467
Description
Environment
- Qiskit version: main c61d797
- Python version: 3.12.10
- Operating system: macOS 15.5
What is happening?
When the main branch of Qiskit attempts to load a QPY file generated by Qiskit 1.2 that contains a parameter expression with a backslash \, it raises an error.
How can we reproduce the issue?
# qpy_dump.py
from qiskit import QuantumCircuit, __version__
from qiskit.circuit import Parameter
from qiskit.qpy import dump
print(f"qiskit_version={__version__}")
qc = QuantumCircuit(2)
alpha = Parameter(r"\alpha")
beta = Parameter(r"\beta")
qc.rz(alpha + beta, 0)
print(qc.draw("text", idle_wires=False))
with open("tmp.qpy", "wb") as file:
dump(qc, file)# qpy_load.py
from qiskit import __version__
from qiskit.qpy import load
print(f"qiskit_version={__version__}")
with open("tmp.qpy", "rb") as file:
qc = load(file)[0]
print(qc.draw("text", idle_wires=False))$ activate qiskit-1.2
$ python qpy_dump.py
qiskit_version=1.2.4
┌────────────────────┐
q_0: ┤ Rz(\alpha + \beta) ├
└────────────────────┘
$ # OK
$ activate qiskit-2
$ python qpy_load.py
qiskit_version=2.0.1
┌────────────────────┐
q_0: ┤ Rz(\alpha + \beta) ├
└────────────────────┘
$ # NG
$ activate qiskit-main
$ python qpy_load.py
qiskit_version=2.1.0.dev0+c61d797
Traceback (most recent call last):
File "/Users/ima/tasks/5_2025/scripts/2025/terra/qpy_load.py", line 6, in <module>
qc = load(file)[0]
^^^^^^^^^^
File "/Users/ima/tasks/5_2025/qiskit/terra/qiskit/qpy/interface.py", line 337, in load
loader(
File "/Users/ima/tasks/5_2025/qiskit/terra/qiskit/qpy/binary_io/circuits.py", line 1425, in read_circuit
_read_instruction(
File "/Users/ima/tasks/5_2025/qiskit/terra/qiskit/qpy/binary_io/circuits.py", line 297, in _read_instruction
param = _loads_instruction_parameter(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/ima/tasks/5_2025/qiskit/terra/qiskit/qpy/binary_io/circuits.py", line 201, in _loads_instruction_parameter
param = value.loads_value(
^^^^^^^^^^^^^^^^^^
File "/Users/ima/tasks/5_2025/qiskit/terra/qiskit/qpy/binary_io/value.py", line 1102, in loads_value
return common.data_from_binary(
^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/ima/tasks/5_2025/qiskit/terra/qiskit/qpy/common.py", line 264, in data_from_binary
obj = deserializer(container, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/ima/tasks/5_2025/qiskit/terra/qiskit/qpy/binary_io/value.py", line 557, in _read_parameter_expression_v3
return ParameterExpression(symbol_map, str(expr_))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/ima/tasks/5_2025/qiskit/terra/qiskit/circuit/parameterexpression.py", line 138, in __init__
self._symbol_expr = SymbolExpr.Expression(expr)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: 0: at line 1:
\alpha + \beta
^
expected '(', found \
1: at line 1, in Alt:
\alpha + \beta
^
2: at line 1, in Permutation:
\alpha + \beta
^
3: at line 1, in Permutation:
\alpha + \beta
^
4: at line 1, in Permutation:
\alpha + \beta
^What should happen?
No error as same as 2.0.1
Any suggestions?
No response