Fix bad deprecation of Register.name_format (#9494) (#9497)

* Fix bad deprecation of Register.name_format

This inadvertantly made the class attribute accessible only from
instances.  It's no use for this to only be on instances, since you
historically needed to validate against the regex to be sure the
instance initialisation would succeed.

* Use custom descriptor instead of classmethod/property

The positive interaction between `classmethod` and `property` was
apparently only added in Python 3.9.

* Fixup release note

Co-authored-by: Matthew Treinish <[email protected]>

---------

Co-authored-by: Matthew Treinish <[email protected]>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
(cherry picked from commit 06f5ac1)

Co-authored-by: Jake Lishman <[email protected]>

qiskit/circuit/register.py

@@ -17,33 +17,35 @@
 """
 import re
 import itertools
+import warnings
 import numpy as np
 
 from qiskit.circuit.exceptions import CircuitError
 
-# Over-specific import to avoid cyclic imports.
-from qiskit.utils.deprecation import deprecate_function
+
+class _NameFormat:
+    REGEX = re.compile("[a-z][a-zA-Z0-9_]*")
+
+    def __get__(self, obj, objtype=None):
+        warnings.warn(
+            "Register.name_format is deprecated as of Qiskit Terra 0.23, and will be removed in a"
+            " future release. There is no longer a restriction on the names of registers, so the"
+            " attribute has no meaning any more.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        return self.REGEX
 
 
 class Register:
     """Implement a generic register."""
 
     __slots__ = ["_name", "_size", "_bits", "_bit_indices", "_hash", "_repr"]
 
-    _name_format = re.compile("[a-z][a-zA-Z0-9_]*")
-
     # In historical version of Terra, registers' name had to conform to the OpenQASM 2 specification
     # (see appendix A of https://arxiv.org/pdf/1707.03429v2.pdf), and this regex enforced it.  That
     # restriction has been relaxed, so this is no longer necessary.
-    @property
-    @deprecate_function(
-        "Register.name_format is deprecated as of Qiskit Terra 0.23, and will be removed in a"
-        " future release. There is no longer a restriction on the names of registers, so the"
-        " attribute has no meaning any more."
-    )
-    def name_format(self):
-        # pylint: disable=missing-function-docstring
-        return self._name_format
+    name_format = _NameFormat()
 
     # Counter for the number of instances in this class.
     instances_counter = itertools.count()

releasenotes/notes/fix-register-name-format-deprecation-61ad5b06d618bb29.yaml

@@ -0,0 +1,10 @@
+---
+fixes:
+  - |
+    Fixed a bad deprecation of :attr:`.Register.name_format` which had made the class attribute
+    available only from instances and not the class.  When trying to send dynamic-circuits jobs to
+    hardware backends, this would frequently cause the error::
+
+      AttributeError: 'property' object has no attribute 'match'
+
+    Fixed `#9493 <https://github.com/Qiskit/qiskit-terra/issues/9493>`__.

test/python/circuit/test_register.py

@@ -120,3 +120,15 @@ def test_newstyle_register_eq(self, reg_type):
         bits_difftype = [difftype.bit_type() for _ in range(3)]
         reg_difftype = difftype(name="foo", bits=bits_difftype)
         self.assertNotEqual(reg_difftype, test_reg)
+
+    @data(QuantumRegister, ClassicalRegister, AncillaRegister)
+    def test_register_name_format_deprecation(self, reg_type):
+        """Test that the `Register.name_format` class data can be accessed and triggers its
+        deprecation correctly."""
+        # From instance:
+        reg_inst = reg_type(2)
+        with self.assertWarnsRegex(DeprecationWarning, "Register.name_format is deprecated"):
+            self.assertTrue(reg_inst.name_format.match("name"))
+        # From class:
+        with self.assertWarnsRegex(DeprecationWarning, "Register.name_format is deprecated"):
+            self.assertTrue(reg_type.name_format.match("name"))