qiskit/releasenotes/notes/0.25/new-circuit-qasm2-methods-b...

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---
upgrade:
- |
The OpenQASM 2 constructor methods on :class:`.QuantumCircuit`
(:meth:`~.QuantumCircuit.from_qasm_str` and :meth:`~.QuantumCircuit.from_qasm_file`) have been
switched to use the Rust-based parser added in Qiskit Terra 0.24. This should result in
significantly faster parsing times (10 times or more is not uncommon) and massively reduced
intermediate memory usage.
The :class:`.QuantumCircuit` methods are kept with the same interface for continuity; the
preferred way to access the OpenQASM 2 importer is to use :func:`.qasm2.load` and
:func:`.qasm2.loads`, which offer an expanded interface to control the parsing and construction.
fixes:
- |
The OpenQASM 2 circuit-constructor methods (:meth:`.QuantumCircuit.from_qasm_str` and
:meth:`~.QuantumCircuit.from_qasm_file`) will no longer error when encountering a ``gate``
definition that contains ``U`` or ``CX`` instructions. See `#5536
<https://github.com/Qiskit/qiskit-terra/issues/5536>`__.