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Fix IPython import issue#19597

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QuLogic merged 2 commits intomatplotlib:masterfrom
Bolton-and-Menk-GIS:ipython_fix
Mar 1, 2021
Merged

Fix IPython import issue#19597
QuLogic merged 2 commits intomatplotlib:masterfrom
Bolton-and-Menk-GIS:ipython_fix

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@philnagel
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@philnagel philnagel commented Feb 27, 2021

When blocking import of IPython by defining sys.modules["IPython"] = None, creating plots fails because backend_bases.FigureCanvasBase._fix_ipython_backend2gui attempts to check if IPython is already imported by looking for an entry in sys.modules. It then attempts to import IPython, which fails due to the import being blocked.

Code sample to reproduce the issue:

import sys
sys.modules['IPython'] = None

from matplotlib import pyplot
plt = pyplot.subplots(1,1)

which results in:

Traceback (most recent call last):
  File "<module1>", line 5, in <module>
  File "C:\Users\Phil\envs\mp_dev\lib\site-packages\matplotlib\cbook\deprecation.py", line 451, in wrapper
    return func(*args, **kwargs)
  File "C:\Users\Phil\envs\mp_dev\lib\site-packages\matplotlib\pyplot.py", line 1287, in subplots
    fig = figure(**fig_kw)
  File "C:\Users\Phil\envs\mp_dev\lib\site-packages\matplotlib\pyplot.py", line 687, in figure
    figManager = new_figure_manager(num, figsize=figsize,
  File "C:\Users\Phil\envs\mp_dev\lib\site-packages\matplotlib\pyplot.py", line 315, in new_figure_manager
    return _backend_mod.new_figure_manager(*args, **kwargs)
  File "C:\Users\Phil\envs\mp_dev\lib\site-packages\matplotlib\backend_bases.py", line 3493, in new_figure_manager
    fig = fig_cls(*args, **kwargs)
  File "C:\Users\Phil\envs\mp_dev\lib\site-packages\matplotlib\figure.py", line 341, in __init__
    FigureCanvasBase(self)  # Set self.canvas.
  File "C:\Users\Phil\envs\mp_dev\lib\site-packages\matplotlib\backend_bases.py", line 1686, in __init__
    self._fix_ipython_backend2gui()
  File "C:\Users\Phil\envs\mp_dev\lib\site-packages\matplotlib\backend_bases.py", line 1713, in _fix_ipython_backend2gui
    import IPython
ModuleNotFoundError: import of IPython halted; None in sys.modules

This PR addresses this issue by not only checking if IPython is present in sys.modules, but also if it is blocked from being imported.

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tacaswell commented Feb 28, 2021

Well, I just learned something about the expected behavior of sys.modules (could not quickly find documentation of this, but found a bug report where CPython made sure this behavior worked as expected https://bugs.python.org/issue31642 which is good enough for me).

@tacaswell tacaswell added this to the v3.4.0 milestone Feb 28, 2021
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tacaswell commented Feb 28, 2021

This suggests we should make a similar change in qt_compat.py where we try to sort out if any of the Qt frameworks are imported already.

anntzer
anntzer reviewed Feb 28, 2021
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@anntzer anntzer mentioned this pull request Feb 28, 2021
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@QuLogic QuLogic merged commit b0aab9f into matplotlib:master Mar 1, 2021
meeseeksmachine pushed a commit to meeseeksmachine/matplotlib that referenced this pull request Mar 1, 2021
@QuLogic @meeseeksmachine
Backport PR matplotlib#19597: Fix IPython import issue
a0b2949
@meeseeksmachine meeseeksmachine mentioned this pull request Mar 1, 2021
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QuLogic commented Mar 1, 2021

Thanks @philnagel! Congratulations on your first PR to Matplotlib 🎉 We hope to hear from you again.

QuLogic added a commit that referenced this pull request Mar 2, 2021
@QuLogic
Merge pull request #19614 from meeseeksmachine/auto-backport-of-pr-19…
3c11289 
…597-on-v3.4.x

Backport PR #19597 on branch v3.4.x (Fix IPython import issue)
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