fix: _isnotebook() recognises JupyterLite, and Colab by its module

src/machinevisiontoolbox/base/imageio.py

@@ -1053,17 +1053,23 @@ def _isnotebook() -> bool:
     """
     Determine if code is being run from a Jupyter notebook
 
-    ``_isnotebook`` is True if running Jupyter notebook, else False
+    ``_isnotebook`` is True if running Jupyter notebook, JupyterLite, Google Colab,
+    or similar, else False
 
     :references:
 
         - https://stackoverflow.com/questions/15411967/how-can-i-check-if-code-
           is-executed-in-the-ipython-notebook/39662359#39662359
     """
+    # JupyterLite runs in the browser, and Colab's shell is google.colab._shell.Shell
+    # rather than a ZMQInteractiveShell; neither is recognised by the shell test below
+    if sys.platform == "emscripten" or "google.colab" in sys.modules:
+        return True
+
     try:
         shell = get_ipython().__class__.__name__  # type: ignore[name-defined]
-        if shell in ("Shell", "ZMQInteractiveShell"):
-            return True  # Jupyter notebook or qtconsole or CoLab
+        if shell == "ZMQInteractiveShell":
+            return True  # Jupyter notebook or qtconsole
         elif shell == "TerminalInteractiveShell":
             return False  # Terminal running IPython
         else:

tests/test_isnotebook.py

@@ -0,0 +1,62 @@
+"""``_isnotebook`` decides how ``Camera`` reuses its image plane, so it has to
+recognise every environment a notebook runs in.  These use a fake ``get_ipython`` and
+patched ``sys.modules`` / ``sys.platform``: no real Jupyter, Colab or JupyterLite
+kernel is exercised."""
+
+import builtins
+import sys
+import types
+
+import pytest
+
+from machinevisiontoolbox.base.imageio import _isnotebook
+
+
+@pytest.fixture
+def plain(monkeypatch):
+    """Standard interpreter: no IPython, not Colab, not Pyodide"""
+    monkeypatch.delattr(builtins, "get_ipython", raising=False)
+    monkeypatch.delitem(sys.modules, "google.colab", raising=False)
+    monkeypatch.setattr(sys, "platform", "linux")
+    return monkeypatch
+
+
+def _shell(monkeypatch, name):
+    shell = type(name, (), {})()
+    monkeypatch.setattr(builtins, "get_ipython", lambda: shell, raising=False)
+
+
+def test_a_standard_interpreter_is_not_a_notebook(plain):
+    assert _isnotebook() is False
+
+
+def test_a_jupyter_kernel_is_a_notebook(plain):
+    _shell(plain, "ZMQInteractiveShell")
+
+    assert _isnotebook() is True
+
+
+def test_ipython_in_a_terminal_is_not_a_notebook(plain):
+    _shell(plain, "TerminalInteractiveShell")
+
+    assert _isnotebook() is False
+
+
+def test_colab_is_a_notebook(plain):
+    plain.setitem(sys.modules, "google.colab", types.ModuleType("google.colab"))
+    _shell(plain, "Shell")
+
+    assert _isnotebook() is True
+
+
+def test_jupyterlite_is_a_notebook_whatever_its_shell_is_called(plain):
+    plain.setattr(sys, "platform", "emscripten")
+    _shell(plain, "SomeOtherShell")
+
+    assert _isnotebook() is True
+
+
+def test_an_unknown_shell_is_not_a_notebook(plain):
+    _shell(plain, "Shell")  # not Colab: google.colab is not loaded
+
+    assert _isnotebook() is False