Python Flake8 linter workflow to replace stickler-ci

.github/workflows/flake8-linter-matcher.json

@@ -0,0 +1,17 @@
+{
+    "problemMatcher": [
+        {
+            "owner": "flake8-linter-error",
+            "severity": "error",
+            "pattern": [
+                {
+                    "regexp": "^([^:]+):(\\d+):(\\d+):\\s+([EWCNF]\\d+\\s+.+)$",
+                    "file": 1,
+                    "line": 2,
+                    "column": 3,
+                    "message": 4
+                }
+            ]
+        }
+    ]
+}

.github/workflows/flake8.yml

@@ -0,0 +1,27 @@
+name: Python Flake8 Linter
+on:
+  pull_request:
+jobs:
+  flake8-linter:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout source
+        uses: actions/checkout@v3
+      - name: Install Python 3.11
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.11'
+      - name: Install Flake8 5.0.4 linter
+        run: pip install flake8==5.0.4  # use this version for --diff option
+      - name: Setup Flake8 output matcher for PR annotations
+        run: echo '::add-matcher::.github/workflows/flake8-linter-matcher.json'
+      - name: Fetch pvlib main branch
+        run: |
+          git remote add upstream https://github.com/pvlib/pvlib-python.git
+          git fetch upstream main
+      - name: Run Flake8 linter
+        run: git diff upstream/main HEAD | flake8
+          --exclude pvlib/version.py
+          --ignore E201,E241,E226,W503,W504
+          --max-line-length 79
+          --diff

pvlib/singlediode.py

@@ -155,6 +155,7 @@ def bishop88(diode_voltage, photocurrent, saturation_current,
        2010
        :doi:`10.4229/25thEUPVSEC2010-4BV.1.114`
     """
+    I = 10
     # calculate recombination loss current where d2mutau > 0
     is_recomb = d2mutau > 0  # True where there is thin-film recombination loss
     v_recomb = np.where(is_recomb, NsVbi - diode_voltage, np.inf)