Fix ignis without optional requirements installed

.github/workflows/main.yml

@@ -37,6 +37,32 @@ jobs:
           QISKIT_IN_PARALLEL: TRUE
         run: tox -e py
         if: runner.os == 'macOS'
+  tests-no-opt:
+    name: tests-python3.8-no-optional-dependencies
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        python-version: [3.8]
+        os: ["ubuntu-latest"]
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Pip cache
+        uses: actions/cache@v2
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-${{ matrix.python-version }}-pip-tests-${{ hashFiles('setup.py','requirements-dev.txt','constraints.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-${{ matrix.python-version }}-pip-tests-
+            ${{ runner.os }}-${{ matrix.python-version }}-pip-
+            ${{ runner.os }}-${{ matrix.python-version }}
+      - name: Install Deps
+        run: python -m pip install -U tox setuptools virtualenv wheel
+      - name: Install and Run Tests
+        run: tox -e no-opt
   windows-tests:
     name: tests-python${{ matrix.python-version }}-windows
     runs-on: windows-latest

qiskit/ignis/mitigation/expval/base_meas_mitigator.py

@@ -166,13 +166,13 @@ def stddev_upper_bound(self, shots: int = 1, qubits: Optional[List[int]] = None)
         return gamma / np.sqrt(shots)
 
     def plot_assignment_matrix(self,
-                               qubits: Optional[List[int]] = None,
-                               ax: Optional[plt.axes] = None) -> plt.axes:
+                               qubits=None,
+                               ax=None):
         """Matrix plot of the readout error assignment matrix.
 
         Args:
-            qubits: Optional, qubits being measured for operator expval.
-            ax: Optional. Axes object to add plot to.
+            qubits (list(int)): Optional, qubits being measured for operator expval.
+            ax (axes): Optional. Axes object to add plot to.
 
         Returns:
             plt.axes: the figure axes object.
@@ -195,13 +195,13 @@ def plot_assignment_matrix(self,
         return ax
 
     def plot_mitigation_matrix(self,
-                               qubits: Optional[List[int]] = None,
-                               ax: Optional[plt.axes] = None) -> plt.axes:
+                               qubits=None,
+                               ax=None):
         """Matrix plot of the readout error mitigation matrix.
 
         Args:
-            qubits: Optional, qubits being measured for operator expval.
-            ax: Optional. Axes object to add plot to.
+            qubits (list(int)): Optional, qubits being measured for operator expval.
+            ax (plt.axes): Optional. Axes object to add plot to.
 
         Returns:
             plt.axes: the figure axes object.
@@ -247,12 +247,12 @@ def _int_to_bitstring(i, num_qubits=None):
         return label
 
     @staticmethod
-    def _plot_axis(mat: np.ndarray, ax: plt.axes) -> plt.axes:
+    def _plot_axis(mat, ax):
         """Helper function for setting up axes for plots.
 
         Args:
-            mat: the N-qubit matrix to plot.
-            ax: Optional. Axes object to add plot to.
+            mat (np.ndarray): the N-qubit matrix to plot.
+            ax (plt.axes): Optional. Axes object to add plot to.
 
         Returns:
             plt.axes: the figure object and axes object.