Removing qml.from_qasm_file from source code and tests (#5659)

**Context:** ***Part of  deprecations and removals for pennylane-0.37***

**Description of the Change:** Removed `qml.from_qasm_file` in favor of
more specific functions.

[sc-58985]

doc/development/deprecations.rst

@@ -50,16 +50,16 @@ Other deprecations
   - Deprecated in v0.36
   - Will be removed in v0.37
 
-* ``qml.from_qasm_file`` is deprecated. Instead, the user can open the file and then load its content using ``qml.from_qasm``.
+Completed deprecation cycles
+----------------------------
+
+* ``qml.from_qasm_file`` has been removed. Instead, the user can open the file and then load its content using ``qml.from_qasm``.
 
   >>> with open("test.qasm", "r") as f:
   ...     circuit = qml.from_qasm(f.read())
 
   - Deprecated in v0.36
-  - Will be removed in v0.37
-
-Completed deprecation cycles
-----------------------------
+  - Removed in v0.37
 
 * The ``qml.load`` function is a general-purpose way to convert circuits into PennyLane from other
   libraries. It has been removed in favour of the more specific functions ``from_qiskit``, ``from_qasm``, etc.

doc/introduction/circuits.rst

@@ -325,7 +325,6 @@ be loaded by using the following functions:
 
     ~pennylane.from_qiskit
     ~pennylane.from_qasm
-    ~pennylane.from_qasm_file
     ~pennylane.from_pyquil
     ~pennylane.from_quil
     ~pennylane.from_quil_file

doc/introduction/importing_workflows.rst

@@ -36,7 +36,6 @@ differentiate and optimize the circuit using :ref:`quantum-specific optimizers <
 
     ~pennylane.from_pyquil
     ~pennylane.from_qasm
-    ~pennylane.from_qasm_file
     ~pennylane.from_qiskit
     ~pennylane.from_quil
     ~pennylane.from_quil_file

doc/releases/changelog-dev.md

@@ -65,6 +65,9 @@
 
 <h3>Breaking changes 💔</h3>
 
+* ``qml.from_qasm_file`` has been removed. The user can open files and load their content using `qml.from_qasm`.
+  [(#5659)](https://github.com/PennyLaneAI/pennylane/pull/5659)
+
 * ``qml.load`` has been removed in favour of more specific functions, such as ``qml.from_qiskit``, etc.
   [(#5654)](https://github.com/PennyLaneAI/pennylane/pull/5654)
 

pennylane/io.py

@@ -15,13 +15,10 @@
 This module contains functions to load circuits from other frameworks as
 PennyLane templates.
 """
-import warnings
 from collections import defaultdict
 from importlib import metadata
 from sys import version_info
 
-import pennylane as qml
-
 # Error message to show when the PennyLane-Qiskit plugin is required but missing.
 _MISSING_QISKIT_PLUGIN_MESSAGE = (
     "Conversion from Qiskit requires the PennyLane-Qiskit plugin. "
@@ -450,43 +447,6 @@ def from_qasm(quantum_circuit: str):
     return plugin_converter(quantum_circuit)
 
 
-def from_qasm_file(qasm_filename: str):
-    """Loads quantum circuits from a QASM file using the converter in the
-    PennyLane-Qiskit plugin.
-
-    **Example:**
-
-    >>> my_circuit = qml.from_qasm_file("hadamard_circuit.qasm")
-
-    The ``my_circuit`` template can now be used within QNodes, as a
-    two-wire quantum template.
-
-    >>> @qml.qnode(dev)
-    >>> def circuit(x):
-    >>>     qml.RX(x, wires=1)
-    >>>     my_circuit(wires=(1, 0))
-    >>>     return qml.expval(qml.Z(0))
-
-    Args:
-        qasm_filename (str): path to a QASM file containing a valid quantum circuit
-
-    Returns:
-        function: the PennyLane template created based on the QASM file
-
-    .. warning::
-        qml.from_qasm_file is deprecated and will be removed in a future release.
-        Please use qml.from_qasm instead.
-
-    """
-    warnings.warn(
-        "qml.from_qasm_file is deprecated and will be removed in a future release. "
-        "Please use qml.from_qasm instead.",
-        qml.PennyLaneDeprecationWarning,
-    )
-    plugin_converter = plugin_converters["qasm_file"].load()
-    return plugin_converter(qasm_filename)
-
-
 def from_pyquil(pyquil_program):
     """Loads pyQuil Program objects by using the converter in the
     PennyLane-Rigetti plugin.

tests/test_io.py

@@ -14,7 +14,7 @@
 """
 Unit tests for the :mod:`pennylane.io` module.
 """
-from unittest.mock import Mock, mock_open, patch
+from unittest.mock import Mock
 
 import pytest
 
@@ -109,14 +109,6 @@ def test_qiskit_converter_load_fails(self, monkeypatch, method, entry_point_name
         with pytest.raises(ValueError, match=r"Some Other Error"):
             method("Test")
 
-    def test_from_qasm_file_deprecated(self, monkeypatch):
-        """Tests that qml.from_qasm_file is deprecated."""
-        mock_converter_dict = {entry: MockPluginConverter(entry) for entry in load_entry_points}
-        monkeypatch.setattr(qml.io, "plugin_converters", mock_converter_dict)
-        with pytest.warns(qml.PennyLaneDeprecationWarning, match="deprecated"):
-            with patch("builtins.open", mock_open(read_data="Test")):
-                _ = qml.from_qasm_file("test.qasm")
-
     @pytest.mark.parametrize(
         "method, entry_point_name",
         [