Fix instruction inheritance issues (#1908)

* fix BasicAer sampling bug (#1624) (#1859)

* fix BasicAer sampling bug (#1624)

* fix BasicAer sampling bug

* changelog

* remove legacysimulator from test_compile

Conflicts:
    CHANGELOG.rst
    test/python/tools/test_compiler.py

The changelog conflicts were inevitable as the stable branch doesn't
have the same history as master. As for the test conflict it was a
difference in the simulator (python vs c++) used, this backport
switches to use the python like on master.

(cherry picked from commit 5f7b2e7)

* Try pinning isort version

* Use constraints from last working version of lint

* Add requirements constraints too

* Bump version and prepare for 0.7.1 release (#1886)

* Bump version and prepare for 0.7.1 release

To prepare for the 0.7.1 bugfix release we need to increase the version
number and update the changelog. This commit takes care of that so we
can tag the release and build it.

* Addressed issue with instruction.py which prohibited inheritance of QuantumRegisters and ClassicalRegisters

* Updated changelog

* Fixed typo

* Reverted changes from merge with Stable

* Fixed changelog

CHANGELOG.rst

@@ -16,10 +16,10 @@ The format is based on `Keep a Changelog`_.
   - **Fixed**: for any bug fixes.
   - **Security**: in case of vulnerabilities.
 
-
 `UNRELEASED`_
 =============
 
+
 Added
 -----
 
@@ -87,6 +87,7 @@ Deprecated
 Fixed
 -----
 
+- Fixed #1892, whereby inheriting from QuantumRegister or ClassicalRegister would cause a QiskitError in instruction.py
 - Fixed #829 by removing dependence on scipy unitary_group (#1857).
 - Fixed a bug with measurement sampling optimization in BasicAer
   qasm_simulator (#1624).

qiskit/circuit/instruction.py

@@ -48,9 +48,9 @@ def __init__(self, name, params, qargs, cargs, circuit=None):
         Raises:
             QiskitError: when the register is not in the correct format.
         """
-        if not all((type(i[0]), type(i[1])) == (QuantumRegister, int) for i in qargs):
+        if not all(isinstance(i[0], QuantumRegister) and isinstance(i[1], int) for i in qargs):
             raise QiskitError("qarg not (QuantumRegister, int) tuple")
-        if not all((type(i[0]), type(i[1])) == (ClassicalRegister, int) for i in cargs):
+        if not all(isinstance(i[0], ClassicalRegister) and isinstance(i[1], int) for i in cargs):
             raise QiskitError("carg not (ClassicalRegister, int) tuple")
         self.name = name
         self.params = []  # a list of gate params stored