BUG: fix IPython's %pylab mode detection

dnicolodi · dnicolodi · commit fffeb9bf6b01 · 2023-03-19T21:33:11.000+01:00
There is no pyplot module in the system registry, as the module is imported as matplotlib.pyplot. This code tries to detect when matplotlib.pyplot.show() is invoked in a script run via the %run IPython's magic while in interactive mode as enabled by the %pylab or %matplotlib IPyhton's magic commands. In these modes, matplotlib.pyplot.show() should not block. Failing do detect these modes, a simple test.py script as this import matplotlib.pyplot as plt plt.figure() plt.show() run in IPython as follows %matplotlib %run test.py is not expected to block on matplotlib.pyplot.show(). Without this patch it does. Additionally, the redraw implemented by IPython at the end of %run caused an empty figure to be displayed when the script terminates. Fixing the module lookup in sys.modules fixes the issue. Fixes 86f26a0. Fixes #25485.
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -2930,8 +2930,8 @@ def pyplot_show(cls, *, block=None):
             # Hack: Are we in IPython's %pylab mode?  In pylab mode, IPython
             # (>= 0.10) tacks a _needmain attribute onto pyplot.show (always
             # set to False).
-            ipython_pylab = hasattr(
-                getattr(sys.modules.get("pyplot"), "show", None), "_needmain")
+            pyplot_show = getattr(sys.modules.get("matplotlib.pyplot"), "show", None)
+            ipython_pylab = hasattr(pyplot_show, "_needmain")
             block = not ipython_pylab and not is_interactive()
         if block:
             cls.start_main_loop()
@@ -3645,8 +3645,8 @@ def show(cls, *, block=None):
             # Hack: Are we in IPython's %pylab mode?  In pylab mode, IPython
             # (>= 0.10) tacks a _needmain attribute onto pyplot.show (always
             # set to False).
-            ipython_pylab = hasattr(
-                getattr(sys.modules.get("pyplot"), "show", None), "_needmain")
+            pyplot_show = getattr(sys.modules.get("matplotlib.pyplot"), "show", None)
+            ipython_pylab = hasattr(pyplot_show, "_needmain")
             block = not ipython_pylab and not is_interactive()
         if block:
             cls.mainloop()
