Fix incompatibility with matplotlib 3.5.0-3.9.x

.github/workflows/main.yml

@@ -26,11 +26,23 @@ jobs:
       matrix:
         os: [ubuntu-latest]
         python-version: ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"]
+        matplotlib-version: [""]
+        numpy-version: [""]
         include:
           #- os: macos-latest
           #  python-version: "3.14"
           - os: windows-latest
             python-version: "3.14"
+            matplotlib-version: ""
+            numpy-version: ""
+          - os: ubuntu-latest
+            python-version: "3.9"
+            matplotlib-version: "==3.5.0"
+            numpy-version: "<2"
+          - os: ubuntu-latest
+            python-version: "3.12"
+            matplotlib-version: "<3.10.0"
+            numpy-version: ""
 
     steps:
     - name: Checkout
@@ -45,9 +57,9 @@ jobs:
 
     - name: Install package with test dependencies
       # matplotlib is not a dependency but tests need it
-      run: |
-        pip install .[test]
-        pip install matplotlib
+      run: >-
+        pip install ".[test]" "matplotlib${{ matrix.matplotlib-version }}"
+        "numpy${{ matrix.numpy-version }}"
 
     - name: Test installation without nbdime
       run: pytest -v

matplotlib_inline/backend_inline.py

@@ -212,8 +212,11 @@ def _enable_matplotlib_integration():
 
     import matplotlib
 
-    if matplotlib.__version_info__ >= (3, 10):
+    version = matplotlib.__version_info__
+    if version >= (3, 10):
         backend = matplotlib.get_backend(auto_select=False)
+    elif version >= (3, 5):
+        backend = matplotlib.get_backend()
     else:
         backend = matplotlib.rcParams._get("backend")
 

tests/test_import.py

@@ -1,4 +1,28 @@
+import pytest
+
+
 def test_import():
     from matplotlib_inline.backend_inline import show
 
     show()
+
+
+@pytest.mark.parametrize("version", [(3, 5, 0), (3, 9, 9)])
+def test_enable_matplotlib_integration_before_3_10_uses_legacy_get_backend(
+    monkeypatch, version
+):
+    from matplotlib_inline import backend_inline
+
+    calls = []
+
+    def get_backend():
+        calls.append(None)
+        return "agg"
+
+    monkeypatch.setattr(backend_inline.matplotlib, "__version_info__", version)
+    monkeypatch.setattr(backend_inline.matplotlib, "get_backend", get_backend)
+    monkeypatch.setattr(backend_inline, "get_ipython", lambda: None)
+
+    backend_inline._enable_matplotlib_integration()
+
+    assert calls == [None]