qiskit/releasenotes/notes/1.0/remove-legacy-qasm2-parser-...

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---
upgrade_qasm:
- |
The legacy OpenQASM 2 parser module previously present in ``qiskit.qasm`` has
been removed. It was marked as deprecated in Qiskit 0.46.0 release. The
OpenQASM 2 parser has been superseded by the :mod:`qiskit.qasm2` module which
provides a faster and more correct parser for QASM2.
- |
The ``qiskit.converters.ast_to_dag`` function has been removed. It
previously was used to convert the abstract syntax tree generated by the
legacy OpenQASM 2 parser (in the ``qiskit.qasm`` module which no longer exists)
and convert that directly to a :class:`.DAGCircuit`. This function was
marked as deprecated in the Qiskit 0.46.0 release. As the legacy
OpenQASM 2 parser has been removed, this function no longer serves a purpose.
If you were previously using this, you can instead parse your OpenQASM 2 files
into a :class:`.QuantumCircuit` using the
:meth:`.QuantumCircuit.from_qasm_file` or
:meth:`.QuantumCircuit.from_qasm_str` constructor methods and then
converting that :class:`.QuantumCircuit` into a :class:`.DAGCircuit` with
:func:`.circuit_to_dag`.
upgrade_circuits:
- |
Removed the ``QuantumCircuit.qasm()`` method to generate a OpenQASM 2
representation of the :class:`.QuantumCircuit` object. Instead the
:func:`.qasm2.dump` or :func:`.qasm2.dumps` functions should be used. This
function was marked as deprecated in the 0.46.0 release. If you were using
the ``QuantumCircuit.qasm()`` method to generate pygments-formatted output
you should instead look at the standalone ``openqasm-pygments`` package
to provide this functionality.
upgrade_misc:
- |
Removed the ``qiskit.tools.jupyter.library.qasm_widget`` function which
was used to visualize OpenQASM 2 strings in a Jupyter notebook. This function
was marked as deprecated as part of the Qiskit 0.44.0 release. The function
was originally used for building documentation but hasn't been used in some
time and has been removed from Qiskit.